Protein denaturation

Chemical terminology

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protein Protein denaturation Natural protein is affected by physical or chemical factors, and the original specific conformation within the molecule changes, resulting in partial or complete loss of its properties and functions. This effect is called Denaturation of protein 。

Chinese name: Protein denaturation
Foreign name: protein denaturation
Discipline: Biology

Denaturation cause: Protein is affected by physical or chemical factors
Denaturation result: Loss of protein activity
influence factor: proton

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protein

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Protein is composed of amino acid adopt Peptide bond Constitutive Polymer compound , respectively in protein molecules amino Acid passes through peptide bond and Disulfide bond Combined into a certain order Peptide chain be called Primary structure ； protein The amino groups and acyl The main chain of this polypeptide chain has a regular conformation, including α- screw 、 β- fold 、 β- corner And omega rings, which are called protein Secondary structure ； The peptide chain further twists and folds on the basis of the secondary structure to form a complete spatial conformation, called Tertiary structure ； Multiple peptide chains pass through Noncovalent bond Aggregated space structure be called Four level structure One of the peptide chains is called a Subunit 。

Denaturation cause

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Protein denaturation

Denaturation It is the effect of physical or chemical factors on protein to change its internal structure and properties. It is generally believed that the secondary structure and tertiary structure of the protein have changed or been damaged, which is the result of denaturation. Chemical methods that can denature protein include strengthening acid, strong base, heavy metal salt urea 、 acetone Etc; Physical methods that can denature proteins include heating (high temperature) ultraviolet rays and X-ray Irradiation, ultrasonic, violent vibration or stirring, etc.

Denaturation result

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Loss of biological activity

protein Of biological activity It refers to the enzyme hormone , toxin, antigen and antibody hemoglobin And other biological functions. Loss of biological activity is the main feature of protein denaturation. Sometimes protein space structure Only slight changes can cause the loss of biological activity.

Some physical and chemical properties

Protein molecules coagulate and precipitate from solution

After protein denaturation Physical and chemical properties Change, such as solubility Precipitation is generated due to the decrease, because some hydrophobic groups originally inside the molecule are exposed due to loose structure Asymmetry Increase, so the viscosity increases, diffusion coefficient Lower.

Biochemical properties

protein After denaturation, molecular structure Loose, unable to form crystals, easy to be hydrolyzed by protease. Denaturation of protein It is mainly due to the destruction of the internal structure of protein molecules. The spatial structure of natural protein is through hydrogen bonding, etc secondary bond The secondary bond is destroyed after denaturation, and the protein molecule changes from the original ordered curly tight structure to the disordered loose stretching structure (but Primary structure Has not changed). Therefore, a large number of hydrophobic groups originally located inside the molecule are exposed on the molecular surface, and Hydrophilic group The distribution on the surface is relatively reduced, so that the protein particles can not aqueous phase Dissolve and lose the water film, which is easy to cause intermolecular collision and aggregation precipitation.

Mutagenic factor

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The causes of protein denaturation can be divided into physical and chemical factors.

Physical factors can be heating, pressurization, stirring, oscillation Ultraviolet radiation , ultrasonic effect, etc; Chemical factors include dehydration strong acid , strong alkali urea 、 Heavy metal salts 、 Sodium lauryl sulfate (SDS), etc.

Heavy metal salts protein Denaturation due to heavy metals cation It can interact with the free carboxyl It forms insoluble salt, and there are Chemical bond The fracture and generation of Chemical change 。

strong acid Strong bases denature proteins because strong acids and bases can break the hydrogen bond in proteins. It can also be connected with free amino Or carboxyl group forming salt, in the process of change, chemical bonds are also broken and formed, so it can be regarded as a chemical change.

Urea ethanol 、 acetone They can provide their own hydroxyl or carbonyl The hydrogen or oxygen on the protein can form hydrogen bond, thus destroying the original hydrogen bond in the protein and denaturing the protein. However, hydrogen bond is not a chemical bond, and there is no break and formation of chemical bond in the process of change, so it is usually a physical change.

Heating, ultraviolet radiation, violent oscillation, etc Physical methods Denaturate the protein, usually destroying the hydrogen bond in the protein molecule, and there is no Chemical bond Fracture and generation of New substances Generation is generally a physical change.

Can promote protein denaturation * salting out

stay clinical medicine On, denaturation Factors are often applied to disinfection and sterilization. On the contrary, protein preparation can be effectively preserved by preventing protein denaturation. Protein denaturation It is very complicated. To judge whether denaturation is a physical change or a chemical change, it depends on the specific situation. If there is chemical bond breaking and formation, it is a chemical change; If there is no chemical bond, the fracture and formation are physical changes.

Application value

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1. The protein of eggs and meat will be denatured after being heated, and it will be easier to digest after being cooked.

2. Bacteria Viruses Heat, add acid, and inactivate metal (mercury) due to protein denaturation (sterilization, disinfection).

3. Animals Insect specimen Fixed storage and anti-corrosion.

4. Many toxins are proteins, plus formaldehyde Fixed, Attenuation Sealing toxic base groups toxoid Antigens, Preparation Antitoxin 。

5. It is used for precipitation of miscellaneous proteins in protein purification.

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Renaturation

Protein is exposed to light, heat Organic solvent And some Denaturant When the, secondary bond Damaged, resulting in natural conformation The destruction of protein biological activity Loss. If the denaturation condition is severe and lasting, the denaturation of protein is irreversible. If the denaturation condition is not severe, this Denaturation It is reversible, indicating that the internal structure of protein molecule has little change. At this time, if the denaturation factor is removed denatured protein It can restore its natural conformation and biological activity, which is called protein renaturation （renaturation）。 for example Pepsin When heated to 80~90 ℃ Solubility It also has no ability to digest protein. If the temperature is reduced to 37 ℃ again, the solubility and ability to digest protein can be restored.^[1]

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