amino acid

[ ā n j ī su ā n]

Small organic molecules that make up proteins

Collection

zero Useful+1

zero

Amino acid is a kind of alkaline amino And acidity carboxyl Amphoteric organic compound of, which is the basic component unit of biological functional macromolecular protein^[1] 。

Amino acids can be divided into protein amino acids and non protein amino acids. Among them, protein amino acids, also known as standard amino acids, are directly involved in the synthesis of protein molecules. Amino acids can be divided into α-，β-，γ- And other amino acids, but the amino acids that constitute natural proteins in the biological world are α- There are 22 kinds of amino acids, including 20 common amino acids and 2 uncommon amino acids.^[2-3] Non protein amino acids can not be directly involved in protein molecular synthesis, but need to be modified to participate in protein synthesis, such as citrulline, ornithine and hydroxyproline.

Amino acids have different properties, such as isoelectric point and optical activity, due to their different structures and R groups. The detection of amino acids can also be screened and identified according to the different properties. At present, the developed detection methods include spectrophotometry, liquid chromatography, gas chromatography, infrared detection and other methods.

Amino acids are raw materials used to produce antibody proteins, hemoglobin, enzyme proteins, hormone proteins, neurotransmitters and other materials in organisms, and even can be used to provide energy sources for organisms. It can be said that amino acids are the source of all life.

Chinese name: amino acid
Foreign name: amino acid

chemical formula: RCH(NH two )COOH
Interpretation: A class of organic compounds containing amino and carboxyl groups
functional group: Amino and carboxyl groups

catalog

one Research History
▪ find
▪ History of Industrial Development
two Physical and chemical properties
▪ physical property
▪ chemical property
three classification
▪ Protein amino acids and non protein amino acids

▪ Oxidative deamination
▪ Non oxidative deamination
▪ Transamination
▪ Combined deamination
six biosynthesis of aminoacids
seven Detection of amino acids
▪ Spectrophotometry
▪ Determination of Amino Acids by Capillary Electrophoresis

Research History

Announce

edit

find

In 1806, French scientists L.N. Vanquelin and J P. Robiquet from Asparagus (Asparagus) Asparagine (asparagine,Asn)。 In 1827, A. Plisson isolated aspartic acid from asparagine, an extract from the roots of hollyhock (Althaenrosea). In 1868, Ritthausen isolated aspartic acid from protein. Because it was first found in asparagus, it is called aspartic acid.

In 1810, the British scientist W Wollaston found cystine in bladder stones, which is called cystinol in English. Cysteine is half of cystine in English, so it is called cysteine in Chinese.

Leucine (also known as leucine) was first separated from cheese by Proust in 1819. Later, in 1820, Braconot obtained its crystal from the acid hydrolysate of muscle and wool, and named it Leucine. The English name is Leucine, which originates from the Greek word Leuco, meaning 'white'. It is called leucine because it is a white powder and leucine because it is easy to crystallize and has high refractive index and is very shiny.

In 1820, H When Bracannot studied the hydrolysis of gelatin, he separated glycine, which was considered to be a sugar at that time. Later, he found that this "gelatin sugar" contains nitrogen atoms, which is the simplest amino acid, and is called glycine (from Greek, 'glycys', meaning "sweet"). In fact, the sweetness of glycine is 80% of that of sucrose. Glycine is the first amino acid discovered by human beings, and it is also the simplest, non-polar and non optically active amino acid.

In 1856, Von Group Besanez separated valine from the extract of pancreas. Until 1906, Fisher analyzed its chemical structure as 2-amino-3-methylbutyric acid, and named it valine, which originated from valerian. In the same year, Cramer hydrolyzed sericin in sulfuric acid to obtain serine, which is called serine in English. Since this nitrogenous acid is isolated from sericin protein, it is named "serine".

In 1861, a German professor extracted glutamate, the component of monosodium glutamate, from wheat gluten for the first time. In 1908, Kiyoshi Ikeda of Japan decomposed MSG from the juice of kelp and put it on the market for the first time as an artificial condiment. In the past, it was mainly extracted from glutelin, so it was called glutamic acid.

In 1886, Schlus separated and extracted arginine from lupine seedlings. In 1895, Hedin found that arginine existed in mammalian proteins. Because its natural product is abundant in protamine, it is called arginine.

In 1889, when Dreehsel separated lysine from casein hydrolysate, he actually got a mixture of lysine and arginine, named Lytatine. Later, Fisher separated lysine from this Lytatine and named it Lysine.

In 1896, German physician Albrecht Kossel separated histidine from histone for the first time.

In 1901, Fischer first discovered proline in white gelatin. The English scientific name is Pyrrolidone Carboxylic Acid, which is simplified as "Proline". The Chinese name "proline" is because it is an important component of collagen, in which "proline" means dried meat and dried fruit. In the same year, the British Frederick Hopkins and Sydney Cole isolated tryptophan in 1901 when they digested casein with insulin. The English name is Tryptophane, which is derived from Insulin and phane, which means "appearance" in Greek.

In 1935, McCoy was equal to separating and identifying threonine from fibrin cutting products, which is called Threonine in English. Because its structure is similar to threose, it is named threonine.

Since then, other amino acids have been found separately. Around 1900, chemists hydrolyzed different proteins in the laboratory to obtain many different amino acids, namely, substances with the structure of one amino group, one carboxyl group and one side chain, and determined the naming rules of amino acids.

On June 6, 2022, the "source of life" - amino acids were found in the sand samples brought back to the earth by the asteroid probe Hayabusa 2 of the Japan Aerospace Exploration Agency from the asteroid "Dragon Palace". This is the first time that the existence of amino acids has been confirmed outside the Earth. On August 1, 2023, Spanish scientists used the Yebes telescope and the IRAM radio telescope to discover for the first time the important component of amino acids, carbonic acid, in a cloud of gas near the center of the Milky Way Galaxy, which may help reveal how life on Earth was formed^[4] 。

History of Industrial Development

Glutamic acid is the first single amino acid product produced industrially in the world. In 1908, Kikunae Ikeda, the founder of Japanese Ajinomoto Company, accidentally found in the laboratory that a white needle shaped crystal could be extracted from kelp soaking solution, which had a strong taste. The analysis of the results showed that it was a sodium salt of glutamic acid. Ikeda finally found a new way to industrialize the production of Ajinomoto, that is, use the "gluten" left after the wheat flour processing starch as raw material, first hydrolyze it with hydrochloric acid to obtain glutamic acid, then add soda ash to neutralize it, and then obtain food grade sodium glutamate. This is the first example of industrial production of amino acids in the world.

The industrial microbial fermentation developed in the 1960s made the amino acid industry take off. Since then, many commonly used amino acid varieties, such as glutamic acid, lysine, threonine, phenylalanine, etc., can be produced by microbial fermentation, which has greatly increased their output and greatly reduced production costs^[5] 。

Physical and chemical properties

Announce

edit

physical property

Amino acid solids are usually colorless crystals, with a melting point of more than 200 ℃, much higher than that of ordinary organic compounds. Amino acids are generally soluble in water, acid solution and alkali solution, and insoluble or slightly soluble in organic solvents such as ethanol or ether. The solubility of different amino acids in water varies greatly, and the solubility of tyrosine is the smallest. At 25 ℃, only 0.045g of tyrosine is dissolved in 100g of water. Lysine and arginine often exist in the form of hydrochloride, which is very soluble in water, and it is difficult to make crystals due to deliquescence. Different amino acids have different tastes, such as sour, sweet, bitter and fresh. Monosodium glutamate and glycine are the most popular flavorings^[6] 。

(1) Appearance: Most common amino acids are colorless crystals, and the crystal shape varies with the structure of amino acids. For example, L-glutamic acid is tetragonal columnar crystal, and D-glutamic acid is rhombic lamellar crystal.

(2) Melting point: The melting point of amino acid crystal is relatively high, generally at 200~300 ℃. Many amino acids will decompose into amine and CO when reaching or approaching the melting point two 。

(3) Solubility: Most amino acids are soluble in water. The solubility of different amino acids in water is different, for example, lysine, arginine and proline are more soluble, while tyrosine, cysteine and histidine are less soluble. All kinds of amino acids can be dissolved in strong bases and acids. However, amino acids are insoluble or slightly soluble in ethanol.

(4) Taste: Amino acids and their derivatives have a certain taste, such as sour, sweet, bitter, salty, etc. The type of taste is related to the type and three-dimensional structure of amino acids. In terms of three-dimensional structure, generally speaking, the sweetness intensity of D-type amino acids is higher than that of corresponding L-type amino acids.

(5) Light absorption characteristics: 20 common amino acids have no absorption ability to visible light. However, it has relatively small light absorption in the far ultraviolet region (less than 220nm). In the ultraviolet region (220nm~300nm), only tyrosine, tryptophan and phenylalanine have light absorption ability, because their R group contains a benzene ring conjugated double bond system. Phenylalanine has the largest light absorption at 259nm, tyrosine at 278nm, and tryptophan at 279nm. Because proteins generally contain these three amino acids, especially tyrosine, the content of proteins can be quantitatively detected by using the ultraviolet absorption characteristics at 280 nm wavelength^[7] 。 The determination of protein content by spectrophotometry is based on Lambert Beer's law. The absorbance value of protein solution at 280nm is proportional to its concentration^[8] 。

(6) Optical activity: Except glycine, other amino acids have asymmetric C atoms, which can be measured by polarimeter. L-amino acids include serine (Ser), leucine (Leu), proline (Pro), tryptophan (Trp), phenylalanine (Phe), etc. The dextral amino acids include Ala, Ile, Glu, Asp, Val, Lys, Arg, etc^[15] 。

Examples of ultraviolet absorption spectra of several amino acids

chemical property

Amino acids are typical amphoteric compounds because they have both amino and carboxyl groups, and are acidic and alkaline. They are positively charged in acidic solutions and negatively charged in alkaline solutions. Among them, amino groups can undergo acylation reaction, nitrite reaction, reaction with aldehyde, sulfonylation reaction, salifying reaction and other reactions. The carboxyl group can undergo acylation, esterification, decarboxylation and salification under certain conditions^[1] 。

1. Isoelectric point

Because amino acid molecules contain NH that can release protons three + And COO who can accept protons - Negative ions, so amino acids are typical amphoteric electrolytes. Amino acids basically exist in the form of facultative ions or dipole ions in aqueous solutions or crystals.

Isoelectric Point of amino acid: The charged state of amino acid depends on the pH value of the environment. Changing the pH value can make amino acid positively or negatively charged, or make it in the zwitterionic state with equal positive and negative charges, that is, zero net charge. The pH value of the solution when the positive and negative charges of the amino acid are equal, that is, when the net charge is zero, is called the isoelectric point of the amino acid, which is usually expressed in pI.

When the pH of amino acid solution is greater than pI (such as adding alkali) three + Given the proton, the balance shifts to the right. At this time, amino acids mainly exist in the form of anions. If they are in an electric field, they move to the positive pole. Conversely, when the pH of the solution is less than pI (such as adding acid) - Combine the proton to shift the balance to the left. At this time, amino acids mainly exist in the form of cations. If they are in the electric field, they move to the negative pole.

Various amino acids have different isoelectric points due to their different compositions and structures. The isoelectric point of neutral amino acids is less than 7, generally 5.0~6.5. The isoelectric point of acidic amino acids is about 3. The isoelectric values of basic amino acids are 7.58~10.8. Under the action of electric field, charged particles move towards the electrode opposite to their electricity, which is called electrophoresis. Because the relative molecular weight and pI of various amino acids are different, in the same pH buffer solution, different amino acids not only have different charge conditions, but also tend to have different swimming directions and speeds in the electric field. Therefore, based on this difference, the mixture of amino acids can be separated by electrophoresis. For example, when the mixture of aspartic acid and arginine is placed in the center of the electrophoresis support medium (filter paper or gel) and the pH of the solution is adjusted to 6.02 (buffer solution), then aspartic acid (pI=2.98) is negatively charged and moves to the positive pole in the electric field, while arginine (pI=10.76) is positively charged and moves to the negative pole^[9] 。

Calculation of isoelectric point: first, write the dissociation equation, the arithmetic mean value of the logarithm of the apparent dissociation constant at the left and right ends of the zwitterion. Generally, the pI value is equal to half of the sum of two similar pK values.

Forms of amino acids in acidic and alkaline solutions

2. Dissociability

Dissociation principle: the degree of dissociation of carboxyl group is greater than that of amino group, α– The group on C is greater than that on non α– The degree of dissociation of the same group on C. That is, priority separation α– COOH, then others – COOH; And then disintegrate α– NH three + , followed by others – NH two 。

Names, abbreviated symbols, R groups and basic physical properties of common amino acids
Amino acid name	abbreviation	Chinese translation	Branched chain	molecular weight	Isoelectric point value	Carboxyl dissociation constant	Amino dissociation constant	Pkr(R)	R-base
Gly	G	glycine	Hydrophilicity	seventy-five point zero seven	five point nine seven	two point three four	nine point six zero	-	-H
Ala	A	alanine	Hydrophobicity	eighty-nine point zero nine	six	two point three five	nine point eight seven	-	-CH₃
Val	V	valine	Hydrophobicity	one hundred and seventeen point one five	five point nine six	two point two nine	nine point seven two	-	-CH-(CH₃)₂
Leu	L	leucine	Hydrophobicity	one hundred and thirty-one point one seven	five point nine eight	two point three three	nine point seven four	-	-CH₂-CH(CH₃)₂
Ile	I	isoleucine	Hydrophobicity	one hundred and thirty-one point one seven	six point zero two	two point three two	nine point seven six	-	-CH(CH₃)-CH₂-CH₃
Phe	F	Phenylalanine	Hydrophobicity	one hundred and sixty-five point one nine	five point four eight	two point five eight	nine point two four	-	-CH₂-C₆H₅
Trp	W	Tryptophan	Hydrophobicity	two hundred and four point two three	five point eight nine	two point four three	nine point four four	-	-CH₂-C₈NH₆
Tyr	Y	Tyrosine	Hydrophilicity	one hundred and eighty-one point one nine	five point six six	two point two zero	nine point two one 10.07ᶜ	ten point four six	-CH₂-C₆H₄-OH
Asp	D	Aspartate	acidic	one hundred and thirty-three point one zero	two point seven seven	one point eight eight 3.65ᵇ	nine point six zero	three point nine zero	-CH₂-COOH
Asn	N	Asparagine	Hydrophilicity	one hundred and thirty-two point one two	five point four one	two point zero two	eight point eight zero	-	-CH₂-CONH₂
Glu	E	glutamate	acidic	one hundred and forty-seven point one three	three point two two	two point one three 4.32ᵇ	nine point six zero	four point zero seven	-(CH₂)₂-COOH
Lys	K	Lysine	alkalinity	one hundred and forty-six point one nine	nine point seven four	two point one eight	eight point nine five 10.53ᶜ	ten point five four	-(CH₂)₄-NH₂
Gln	Q	glutamine	Hydrophilicity	one hundred and forty-six point one five	five point six five	two point one seven	nine point one three	-	-(CH₂)₂-CONH₂
Met	M	methionine	Hydrophobicity	one hundred and forty-nine point two one	five point seven four	two point one three	nine point two eight	-	-(CH₂)2-S-CH₃
Ser	S	serine	Hydrophilicity	one hundred and five point zero nine	five point six eight	two point one nine	nine point four four	-	-CH₂-OH
Thr	T	threonine	Hydrophilicity	one hundred and nineteen point one two	five point six zero	two point zero nine	nine point one zero	-	-CH(CH₃)-OH
Cys	C	Cysteine	Hydrophilicity	one hundred and twenty-one point one six	five point zero seven	one point eight six	eight point three five	eight point three seven	-CH₂-SH
Pro	P	proline	Hydrophobicity	one hundred and fifteen point one three	six point three zero	one point nine five	ten point six four	-	-C₃H₆
His	H	histidine	alkalinity	one hundred and fifty-five point one six	seven point five nine	one point eight one	six point zero five 9.15ᶜ	six point zero four	-CH two -C three H three N two
Arg	R	Arginine	alkalinity	one hundred and seventy-four point two zero	ten point seven six	one point eight two	eight point nine nine 13.20ᶜ	twelve point four eight	-(CH two ) three -NHC(NH)NH two
Note: ᵇ Non α PK ₐ of carboxyl substituent; ᶜ Non α PK ₐ of basic substituent.^[10]

3. Acid base titration curve

In the process of acid-base titration, the curve drawn by the change law of pH of the system with the degree of titration (generally the amount of titrant added or the titration fraction T) is the acid-base titration curve. Take glycine as an example: when 1mol glycine is dissolved in water, the pH of the solution is 5.97, titrate with standard NaOH and HCl respectively, take the pH value of the solution as the ordinate, and the number of moles of HCl and NaOH added as the abscissa to draw a diagram, and obtain the titration curve. A very important feature of this curve is that there are two inflection points at pH=2.34 and pH=9.60, which are respectively pK1 and pK2 of glycine.

classification

Announce

edit

Amino acids, as the name implies, refer to carboxylic acids containing amino acids. The various proteins in the organism are composed of 20 basic amino acids. L – except glycine α– Amino acid (proline is a kind of L - α– Subamino acid), R – α– The general structural formula of amino acids is shown in the figure below (R group is a variable group):

General structural formula of amino acids

Other than glycine α– All carbon atoms are asymmetric, that is α– The four substituents bonded by carbon atoms are different, so amino acids can have stereoisomers, that is, there are two configurations of D – type and L – type^[8] 。

Protein amino acids and non protein amino acids

Protein amino acid: standard amino acid, which is carried by special tRNA in protein biosynthesis and directly involved in protein molecules, including 20 common amino acids and 2 uncommon amino acids. The 20 common amino acids are: glycine, alanine, valine, leucine, isoleucine, methionine (methionine), proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamate, lysine, arginine, histidine. The two uncommon amino acids are selenocysteine and pyrrolysine. Selenocysteine only exists in selenoproteins, while pyrrolysine only exists in some prokaryotic organisms as a component of some enzymes related to methanogenesis.

Non protein amino acids: they cannot be directly incorporated into protein molecules, or they are the post-translational modification products of protein amino acids. For example: citrulline, ornithine and hydroxyproline.

Classification by side chain group

There are 9 kinds of non-polar amino acids (hydrophobic amino acids): alanine, valine, leucine, isoleucine, proline, phenylalanine, tryptophan, methionine and glycine;

There are 13 polar amino acids (hydrophilic amino acids):

Polar uncharged (neutral amino acid): serine, threonine, cysteine, tyrosine, asparagine, glutamine, selenocysteine, pyrrol-lysine;

Polar positively charged amino acids (basic amino acids): lysine, arginine, histidine;

Polar negatively charged amino acids (acidic amino acids): aspartic acid, glutamic acid^[7] 。

Classification of chemical structure

Aliphatic amino acids: alanine, valine, leucine, isoleucine, methionine, aspartic acid, glutamic acid, lysine, arginine, glycine, serine, threonine, cysteine, asparagine, glutamine, selenocysteine;

Aromatic amino acids: phenylalanine, tyrosine, tryptophan;

Heterocyclic amino acids: tryptophan, histidine, proline, pyrrolysine;

Heterocyclic Subamino Acid: Proline^[8] 。

Nutritional classification

Essential amino acids: These amino acids are called essential amino acids because the human body (or other vertebrates) cannot synthesize independently or the synthesis speed is far from meeting the needs of the body and must be supplied by external food. The requirement of essential amino acids for adults is about 20%~37% of the protein requirement. There are 8 kinds, and their functions are as follows:

Lysine: promotes brain development, is a component of liver and gallbladder, can promote fat metabolism, regulate pineal gland, breast, corpus luteum and ovary, and prevent cell degeneration;

Tryptophan: promote the production of gastric juice and pancreatic juice;

Phenylalanine: participate in eliminating the loss of kidney and bladder functions;

Methionine (methionine): it is involved in the formation of hemoglobin, tissue and serum, and has the function of promoting the spleen, pancreas and lymph;

Threonine: It has the function of transforming some amino acids to achieve balance;

Isoleucine: It is involved in the regulation and metabolism of thymus, spleen and sub brain gland;

Leucine: balance isoleucine;

Valine: acts on corpus luteum, breast and ovary^[8] 。

Semi essential amino acids and conditionally essential amino acids:

Although the human body can synthesize amino acids that usually cannot meet normal needs, they are also called semi essential amino acids or conditionally essential amino acids, mainly arginine and histidine, which are essential amino acids in the growth period of young children. The demand for essential amino acids in human body decreases with the increase of age, and the demand for essential amino acids in adults is significantly lower than that in infants. Its functions are as follows:

Arginine: The compound preparation of arginine and deoxycholic acid (minophen) is an effective drug for treating syphilis, viral jaundice and other diseases.

Histidine: It can be used as biochemical reagent and medicament, and also can be used to treat heart disease, anemia, rheumatoid arthritis, etc.

Non essential amino acids: refer to amino acids that can be synthesized by human (or other vertebrates) themselves from simple precursors and do not need to be obtained from food. Such as glycine, alanine and other amino acids^[8] 。

Function and use

Announce

edit

summary:

Amino acids can play the following roles through metabolism in human body:

① Synthesize tissue proteins and participate in biological functions;

② Ammonia containing substances such as acid, hormone, antibody and creatine;

③ It is converted into carbohydrate and fat as the energy storage material of the body;

④ It is oxidized to carbon dioxide, water and urea to generate energy.

Physiological regulation

The role of protein in food nutrition is obvious, but it cannot be directly used in the human body. Instead, it decomposes high molecular protein into low molecular polypeptides or amino acids through digestion such as enzymes, which are absorbed in the small intestine and enter the liver along the portal vein. Some amino acids are decomposed or synthesized in the liver; The other part of amino acids continue to be distributed to various tissues and organs along with the blood, allowing them to choose and synthesize various specific tissue proteins. Therefore, the human body's need for protein is actually the need for amino acids.

Under normal circumstances, the speed of amino acid entering the blood is almost equal to its output speed, so the content of amino acid in normal human blood is quite constant. If calculated by amino nitrogen, the content of plasma per 100 ml is 4-6 mg, and the content of blood cell per 100 ml is 6.5 ～ 9.6 mg. After a full meal of protein, a large amount of amino acids were absorbed, and the level of amino acids in blood temporarily increased. After 6-7 hours, the content returned to normal. It shows that the metabolism of amino acids in the body is in a dynamic balance, with blood amino acids as its balance hub, and the liver is an important regulator of blood amino acids.

When the quality and amount of protein in the daily diet are appropriate, the amount of nitrogen taken in is equal to the amount of nitrogen excreted from feces, urine and skin, which is called nitrogen balance. In fact, it is the balance between the continuous synthesis and decomposition of proteins and amino acids. The daily protein intake of normal people should be kept within a certain range. When the intake suddenly increases or decreases, the body can still adjust the protein metabolism to maintain nitrogen balance. If you eat too much protein, the balance mechanism will be destroyed if it exceeds the body's ability to regulate. If you don't eat protein at all, the tissue protein in your body will still decompose, and negative nitrogen balance will continue to occur. If you don't supplement it in time, it will cause irreversible damage to your body or even death^[8] 。

Produced by amino acid catabolism α– Ketoacid, with different characteristics, is metabolized along the metabolic pathway of sugar or fat. α– Ketoacid can be re synthesized into new amino acids, or converted into sugar or fat, or enter the tricarboxylic acid cycle, and oxidized into CO two And H two O. And release energy.

Some amino acids produce a group containing one carbon atom during catabolism, including methyl, methylene, methyleneyl, methynyl, cresol and iminomethyl. The main physiological function of one carbon unit is as the raw material for the synthesis of purine and pyrimidine, and it is the link between amino acids and nucleotides.

One carbon unit has the following two characteristics:

① It cannot exist in free form in the organism;

② Tetrahydrofolate acid must be used as the carrier.

Amino acids that can produce one carbon unit include serine, tryptophan, histidine and glycine. In addition, methionine can provide "active methyl" (one carbon unit) through S – adenosylmethionine (SAM), so it can also generate one carbon unit.

Amino acids are also involved in the formation of enzymes, hormones, neurotransmitters and some vitamins in the body. The chemical essence of enzyme is protein, such as amylase, pepsin, cholinesterase, carbonic anhydrase, transaminase, etc. The component of nitrogenous hormone is protein or its derivatives, such as growth hormone, thyroid stimulating hormone, adrenaline, insulin, intestinal stimulating hormone, etc. Some vitamins are converted from amino acids or exist in combination with proteins. Enzymes, hormones and vitamins play a very important role in regulating physiological functions and catalyzing metabolic processes^[8] 。

Medical effect

Amino acids are mainly used in medicine to prepare compound amino acid infusion, and also used as therapeutic drugs to synthesize polypeptide drugs. There are more than 100 kinds of amino acids used as medicine, including 22 kinds of amino acids that constitute proteins and more than 100 kinds of amino acids that constitute non proteins.

The compound preparation composed of various amino acids plays a very important role in modern intravenous nutrition infusion and "element diet" therapy. It plays an active role in maintaining the nutrition of critically ill patients and saving their lives, and has become one of the indispensable medicine varieties in modern medicine.

Amino acids such as glutamic acid, arginine, aspartic acid, cystine, L-dopa, etc. can be used alone to treat some diseases, mainly for liver diseases, gastrointestinal diseases, encephalopathy, cardiovascular diseases, respiratory diseases, and to improve muscle vitality, pediatric nutrition and detoxification. In addition, amino acid derivatives have shown promise in cancer treatment^[8] 。

Material basis of life

Protein is the material basis of life, and life is a form of protein existence. The basic unit of protein is amino acid. If the human body lacks any essential amino acid, it can lead to abnormal physiological function, affect the normal progress of body metabolism, and finally lead to disease. Even if it lacks some nonessential amino acids, it will cause metabolic disorders. For example, arginine and citrulline are very important for the formation of urea; Inadequate intake of cystine will lead to decreased insulin and increased blood sugar. Another example is that after trauma, the demand for cystine and arginine is greatly increased. In case of lack, even if the heat energy is sufficient, the protein cannot be successfully synthesized^[8] 。

Flavoring agent

The requirement of essential amino acids for adults is about 20%~37% of the protein requirement. The role of amino acids in food can not be ignored. Some are flavoring agents, some are nutrition enhancers, and some can play a role in enhancing flavor.

1. Taste of amino acids

Most amino acids have a sense of taste and play the role of sour, sweet, bitter, astringent and other tastes in food. Tryptophan is non-toxic and sweet. It and its derivatives are promising sweeteners. There are also some small water-soluble amino acids with bitter taste, which are the products of protein hydrolysis in food processing.

Glutamic acid mainly exists in plant protein and can be obtained by hydrolysis of wheat gluten. Glutamic acid has sour taste and fresh taste, of which sour taste is the main. When alkali is added to neutralize properly, sodium glutamate is generated; After the formation of salt, the sour taste of glutamic acid disappears and the fresh taste increases. Sodium glutamate is the main component of monosodium glutamate, a widely used flavor agent.

2. One of the prerequisite substances for flavor

The carbonyl ammonia reaction between amino acids and sugars is an important reason for aroma and coloring in food processing. During the reaction, some amino acids and sugars are consumed to produce flavor substances. Amino acids can also be heated and decomposed to produce certain flavor substances, or substances with peculiar smell can be produced under the decomposition of bacteria. Therefore, amino acids are the prerequisite substances for flavor substances and nutrients for putrefactive bacteria^[6] 。

Metabolic pathway

Announce

edit

The metabolism of amino acids is mainly carried out in the liver through the following ways:

Oxidative deamination

The first step is dehydrogenation to generate imine;

The second step is hydrolysis.

H generated in this step two O two Toxic, can generate H under the catalysis of catalase in the body two O and O two To relieve the toxic effect on body cells.

Non oxidative deamination

① Reduction deamination (under strict oxygen free conditions);

② Hydrolytic deamination;

③ Dehydration and deamination;

④ Mercapto deamination;

⑤ Oxidation reduction deamination, where two amino acids react with each other to form organic acids, ketoacids and ammonia;

⑥ Deamidation.

Transamination

Transamination is an important way of amino acid deamination. Except glycine, lysine, proline and threonine, most amino acids can participate in transamination. α– Amino acids and α– Amino transfer occurs between keto acids, resulting in the formation of corresponding keto acids from the original amino acids, and corresponding amino acids from the original keto acids.

Combined deamination

The cells in the body cannot finally deaminate by transamination alone, and oxidative deamination alone cannot meet the needs of the body for deamination, so the body needs to rapidly deaminate by means of combined deamination:

① Joint deamination centered on glutamate dehydrogenase. Amino acid α– Amino first α– On ketoglutaric acid, corresponding α– Ketoacid and Glu, and then deaminase under the catalysis of L – Glu deaminase α– Ketoglutarate and release ammonia.

② Joint deamination through the purine nucleotide cycle. Skeletal muscle, heart muscle, liver and brain are dominated by purine nucleotide circulation.

Most amino acids in the organism can be decarboxylated to produce corresponding primary amines. Amino acid decarboxylase is highly specific. Each amino acid has a decarboxylase, and the coenzyme is pyridoxal phosphate. Amino acid decarboxylation reaction widely exists in animals, plants and microorganisms. Some products have important physiological functions, such as L – Glu decarboxylation in brain tissue to generate r – aminobutyric acid, which is an important neurotransmitter. His decarboxylation produces histamine (also known as histamine), which can reduce blood pressure. Tyr decarboxylates to form tyramine, which has the effect of raising hypertension. However, most amines are toxic to animals. There is amine oxidase in the body, which can oxidize amines into aldehydes and ammonia.

In conclusion, the existence of amino acids in the human body not only provides an important raw material for protein synthesis, but also provides a material basis for promoting growth, normal metabolism and maintaining life. If the human body lacks or reduces one of them, the normal life metabolism of the human body will be hindered, even leading to the occurrence of various diseases or the termination of life activities.

biosynthesis of aminoacids

Announce

edit

Of the 20 basic amino acids, humans can synthesize 11 of them. The other nine amino acids must be taken from food, so they are called essential amino acids, namely phenylalanine, methionine, threonine, tryptophan, lysine, histidine, valine, leucine and isoleucine^[11] 。

In biochemistry, amino acids are classified into five types according to their synthetic pathways: glutamic acid type, aspartic acid type, pyruvate derivative type, serine type and aromatic amino acid type. Most of the amino acids that make up the protein are biosynthesized by the carbon chain skeleton of the intermediate between the Embeden Meyerhof pathway and the citric acid cycle, except aromatic amino acids and histidine. The biosynthesis of aromatic amino acids is related to erythrin-4-phosphate, the intermediate of pentose phosphate, and histidine is synthesized from ATP and phosphoribosyl pyrophosphate.

The essential amino acids are generally biosynthesized by the intermediates of carbohydrate metabolism through multi-step reactions (more than 6 steps). About 14 enzymes are required for the synthesis of nonessential amino acids, while more enzymes are required for the synthesis of essential amino acids, involving about 60 enzymes. In general, some of the steps are simple and some are complex. Higher animals give up the more complicated ones and get them from food instead.

For example, the glutamate type is determined by α- It is derived from ketoglutaric acid, including glutamic acid, glutamine, proline and arginine. The lysine synthesis of mushrooms and Euglena also belongs to this pathway.

Glutamate can be α- Ketoglutarate and ammonia are catalysed by glutamate dehydrogenase, and NADPH is consumed (NADH is generated during deamination). Another way is glutamine and α- Ketoglutarate reacts to form two glutamate, which is catalyzed by glutamate synthase. This method consumes more energy, but the glutamine synthetase Km is low and can react at a lower ammonia concentration, so it is more commonly used.

Synthetic Pathways of Aromatic Amino Acids in Plants^[11]

Detection of amino acids

Announce

edit

There are many methods for the determination of amino acids, such as color reaction, high performance liquid chromatography, liquid chromatography-mass spectrometry, capillary electrophoresis, gas chromatography, etc., which are detailed as follows^[12] ：

Spectrophotometry

It mainly uses the chemical reaction between amino acid and derivative agent to produce a blue purple compound, which has the maximum absorption peak at a certain wavelength, and the amino acid content can be obtained according to the absorption value. The commonly used derivative agent is ninhydrin. Spectrophotometry has the characteristics of easy operation, simple instrument requirements, low cost, wide application range and suitable for the detection of aromatic amino acids.

Determination of Amino Acids by Capillary Electrophoresis

According to the different separation principles, it can be divided into capillary zone electrophoresis, capillary gel electrophoresis, capillary isoelectric electrophoresis, capillary isokinetic electrophoresis and micellar electrokinetic capillary electrophoresis. Among them, capillary zone electrophoresis and micellar electrokinetic capillary electrophoresis can be used for amino acid detection. Capillary electrophoresis has the characteristics of high separation efficiency, short analysis time, less solvent consumption, no gradient elution and suitable for chiral separation of amino acids, but the reproducibility of the analytical results of this method is poor.

Determination of Amino Acids by Near Infrared Spectroscopy

Using the transition of hydrogen containing groups of organic compounds in a specific wavelength region to produce spectral changes, combined with statistical methods, the quantitative detection of amino acids can be achieved indirectly. Near infrared spectroscopy is characterized by high efficiency, non pollution, non destructiveness and simultaneous detection of multi-component.

Determination of amino acids by gas chromatography

The amino acid derivatization is changed into a substance that is easy to gasify, and the quantitative analysis of amino acids is realized according to the different distribution coefficients of each component in the mobile phase and the fixed phase of the gaseous sample. GC method can not only detect the content of amino acids, but also find new amino acids. However, its disadvantages are complex operation, many interference factors and poor specificity.

Determination of Amino Acids by High Performance Liquid Chromatography

It is the most commonly used method for amino acid detection. Since most amino acids do not have UV absorption and fluorescence reaction, the sample needs to be derivatized to convert them into substances with UV absorption and fluorescence emission. The derivatization can be divided into pre column derivatization and post column derivatization.

Partial color reaction and detection principle
Ninhydrin reaction	reagent	Ninhydrin (heated in weak acid environment)
	colour	Purple (proline and hydroxyproline are yellow)
	principle	test α– amino acid
Sakaguchi reaction	reagent	α– Naphthol+basic sodium hypobromate
	colour	gules
	principle	Test guanidine, arginine has this reaction
Millon reaction	reagent	HgNO3+HNO3+(heating)
	colour	gules
	principle	Test the phenolic group, tyrosine has this reaction, and it is white if not heated
Folin – Ciocalteau reaction (phenol reagent reaction)	reagent	Phosphotungstic acid – phosphomolybdic acid
	colour	blue
	principle	Test the phenolic group, and tyrosine has this reaction
Xanthoproteic Reaction	reagent	Concentrated nitric acid (boiled)
	colour	yellow
	principle	Test the benzene ring, tyrosine, phenylalanine and tryptophan have this reaction
Hopkin Cole reaction (glyoxylic acid reaction)	reagent	Glyoxylic acid, concentrated sulfuric acid
	colour	Purplish red
	principle	Test indolyl group, tryptophan has this reaction
Ehrlich reaction	reagent	P-Dimethylaminobenzaldehyde, concentrated hydrochloric acid
	colour	blue
	principle	Test indolyl group, tryptophan has this reaction
Nitroprusside Reaction	reagent	Na2 (NO) Fe (CN) 2 · 2H2O, dilute ammonia
	colour	gules
	principle	Test the sulfhydryl group, cysteine has this reaction
Sullivan reaction	reagent	1, 2 – Naphthoquinone – 4 – Sodium sulfonate, Na2SO3
	colour	gules
	principle	Test the sulfhydryl group, cysteine has this reaction
Folin reaction	reagent	1, 2 – Naphthoquinone – 4 – Sodium sulfonate (alkaline environment)
	colour	oxblood red
	principle	test α– amino acid

Liquid chromatography of 17 amino acids (under the action of phenyl isothiocyanate (PITC) reagent)^[16]

1. Aspartate 2. Glutamate 3. Serine 4. Glycine weight 5. Histidine 6. Arginine 7. Threonine 8. Alanine 9. Proline 10. Ammonia 11. Tyrosine 12. Valine 13. Methionine 14. Cysteine 15. Isoleucine 16. Leucine 17. Phenylalanine 18. Lysine

Related concepts

Announce

edit

Peptide bond: condensation of the carboxyl group of one amino acid with the amino group of another to remove the amide bond formed by a molecule of water.

Peptide: polymer formed by covalent connection of two or more amino acids through peptide bond. It is a compound of amino acids linked by peptide bonds, and the product of incomplete protein hydrolysis is also a peptide. Peptides are called dipeptides, tripeptides and tetrapeptides respectively according to the number of amino acids they consist of: 2, 3 and 4. Oligopeptides generally consist of less than 10 amino acids and polypeptides consist of more than 10 amino acids. They are called peptides for short. The amino acid in the peptide chain is no longer a free amino acid molecule, because its amino and carboxyl groups are combined in the generation of peptide bonds, so the amino acids in the polypeptide and protein molecules are called amino acid residues.

The difference between polypeptides and proteins is that, on the one hand, the amino acid residues in polypeptides are less than those in proteins, generally less than 50, while most proteins are composed of more than 100 amino acid residues, but there is no strict boundary in the number between them. In addition to molecular weight, it is also believed that polypeptides generally have no tight and relatively stable spatial structure, That is, its spatial structure is relatively variable and plastic, while the protein molecule has a relatively tight and stable spatial structure, which is also the basis for the physiological function of protein. Therefore, insulin is generally classified as a protein. However, in some books, insulin is not strictly called polypeptide because of its small molecular weight. However, both peptides and proteins are polycondensates of amino acids, and peptides are also products of incomplete protein hydrolysis^[8] 。

Related research progress

Announce

edit

AI: In 2022, the research of biologists from Washington University School of Medicine showed that machine learning can create protein molecules more accurately and faster than before. The team has designed a new algorithm for generating amino acid sequences, called ProteinMPNN, with a running time of about 1 second, more than 200 times faster than the best software before. It can run without expert customization. This progress is expected to lead to more new vaccines, therapies, carbon capture tools and sustainable biomaterials. Relevant papers published in Science^[13] 。

In the past decade, scientists have found that inhibiting amino acids in animal diets can slow down the growth of certain tumors. Tumors depend on the nonessential amino acids serine and glycine. Serine and glycine are biosynthetically linked. They provide necessary precursors for the synthesis of proteins, lipids and nucleic acids. These substances are critical to the growth of cancer cells, and also support tumor homeostasis. Researchers at the University of California, San Diego and the Salk Institute of Biology have taken a different approach to slow the growth of tumors. Their research was published in the journal Nature^[14] 。

Novice on the road

Growth task Getting Started with Editing Edit Rule Edit by myself

I have questions

Content query Online Service Official post bar Feedback

Complaints and suggestions

Report bad information Failed to appeal through entries Complaint of infringement information Blocking query and unblocking

Jinggong Network Anbei No. 1100000200001