Plasma protein

General name of protein

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Plasma protein refers to the protein part of plasma. Plasma protein is the general name of various proteins. Plasma protein can be divided into several components such as albumin, globulin and fibrinogen. The molecular weight of albumin is the smallest among the three types of proteins, but the content of albumin in plasma is the largest. Plasma protein can be used as animal feed, nutritional supplement, and can be used to extract heme, hematoporphyrin derivatives Superoxide dismutase (SOD) and widely used in meat products.

Chinese name: Plasma protein
Foreign name: Plasma protein
Content: 65～85g/L

molecular weight: ninety
Isoelectric point: pH4～6
separation method: Salt out method, immunoelectrophoresis
Synthesis site: liver

catalog

brief introduction

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Plasma protein is the general name of various proteins in plasma

The concentration of plasma protein is Tissue fluid The main difference is that plasma protein molecules are too large to penetrate blood capillary Pipe wall. In biochemical research Salting out method Divide plasma proteins into albumin 、 Globulin And Fibrinogen Three categories. Later, albumin was divided into albumin and Prealbumin Globulins are divided into α 1-globulin, α 2-globulin, β - globulin, γ - globulin, etc. Use other methods, such as Immunoelectrophoresis And can further distinguish plasma proteins. This indicates that plasma proteins include many proteins with different molecular sizes and structures.

form

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Blood consists of formed red blood cells white blood cell And platelets, as well as the invisible liquid component plasma. Blood coagulation After that, light yellow transparent liquid is precipitated, which is called serum. The difference between serum and plasma is that there is no fibrinogen in serum, but some fibrinogen Coagulation Decomposition products generated in the process.

Under physiological conditions, blood flows continuously throughout the body through blood vessels to transport various substances and tissues. Plasma, interstitial fluid and others Extracellular fluid They together form the internal environment of the body. Therefore, blood plays an important role in communicating the internal and external environment, maintaining the relative stability of the internal environment (such as pH, osmotic pressure, concentration of various chemical components, etc.), material transportation (nutrients, metabolites, metabolic regulators), immune defense, coagulation and anticoagulation.

classification

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Plasma proteins were initially divided into albumin and globulin by salting out method, and later into albumin, globulin, euglobulin, fibrin and other components by segmented salting out method.

use acetate fibre The membrane electrophoresis method can be divided into five zones: albumin, α 1 globulin, α 2 globulin, β - globulin and γ - globulin, while the polyacrylamide gel electrophoresis method with high resolution can be divided into 34 zones.

use Isoelectric focusing electrophoresis And polyacrylamide The two-dimensional electrophoresis of electrophoresis combination has higher resolution and can divide plasma proteins into more than 100 kinds. The simple and fast cellulose acetate membrane electrophoresis method is often used in clinical practice.

Known in recent years Plasma protein There are more than 200 kinds, and the function of some proteins has not been clarified yet.

Classification by function

Plasma proteins are diverse, and various plasma proteins have their unique functions. In addition to classification according to separation methods, functional classification can also be used. It can be divided into the following 8 categories:

① Coagulation system Protein, including 12 coagulation factors (except Ca2+).

② Fibrinolytic system Proteins, including Fibrinolytic enzyme Protamine, plasmin, activator and inhibitor, etc.

③ Complement system protein.

④ immunoglobulin 。

⑤ Lipoprotein.

⑥ Plasma Protease inhibitor , including zymogen activation inhibitors, blood coagulation inhibitors Plasmin inhibitor , kinin release inhibitor endogenous Protease and other protease inhibitors.

⑦ As a carrier combined with various ligands, it has a transport function..

⑧ Plasma protein with unknown function.

Common characteristics

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1. Most plasma proteins are synthesized by the liver. except Gamma globulin from plasma cells synthesis, endothelial cells Synthesis of a small amount of plasma protein.

2. Plasma protein is secretory protein. It is synthesized on the polyribosomes bound to the endoplasmic reticulum and undergoes post-translational modification processes such as shear signal peptide, glycosylation and phosphorylation before being secreted into the plasma, becoming mature proteins.

3. Plasma proteins are almost all glycoprotein , containing N - or O-linked oligosaccharide chains. Albumin only Retinol binding protein And C-reactive protein. Sugar chains can participate in the formation of the tertiary structure of plasma protein molecules and have multiple functions.

4. All plasma proteins have their characteristic circulating half-life.

5. Many plasma proteins have Polymorphism (polymorphism）。 Polymorphism refers to more than two phenotypes with frequency of no less than 1% in the same population. The most typical is ABO blood group Substance. In addition, α 1 Antitrypsin , combination Globin , iron transporter, plasma Ceruloplasmin And so on. The study of plasma protein polymorphism is of great significance to genetics and clinical medicine.

6. When acute inflammation or tissue damage occurs, some plasma protein levels increase. These plasma proteins are called Acute phase protein Acute phase protein. Including C? CRP, α 1 antitrypsin, α 2 acid glycoprotein, fibrinogen, etc. Acute phase protein in human body inflammatory reaction Play a certain role in.

major function

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1. Nutritional function

Each adult has about 200g protein in about 3L plasma, which plays the role of nutrition reserve. Although the digestive tract generally does not absorb protein, it absorbs amino acid However, some cells in the body, especially Monocyte phagocyte system , swallow the complete plasma protein, and then swallow the Proteolysis It is amino acid. The amino acids thus generated diffuse into the blood and can be used by other cells to synthesize new proteins at any time.

2. Transport function

There are many lipophilic binding sites distributed on the huge surface of protein, which can combine with fat tolerant substances, making them water-soluble and easy to transport; Plasma protein can also reversibly combine with substances with small molecules in the blood (such as hormones and various positive ions), which can prevent them from losing from the kidney. Because the substances in the combined state and free state are in dynamic balance, the concentration of these substances in the free state in the blood can be kept relatively stable.

3. Buffer the acid-base changes that may occur in plasma, and maintain the stability of blood pH.

Adjust the pH value of plasma to maintain acid-base balance. Most of the isoelectric points of plasma proteins are at pH4-6, and most of the proteins in plasma exist in the form of negative ions, which constitute buffer pairs in plasma in the form of (Pr represents plasma protein).

4. Formation Colloid osmotic pressure , regulate the water distribution inside and outside the blood vessels, and maintain Plasma colloid osmotic pressure , mainly by Plasma albumin 。

Because of its high content and small molecule, it maintains 75~80% of plasma colloid osmotic pressure.

5. Participate in the immune function of the body

Important in realizing immune function Immune antibody , complement system, etc. are all composed of plasma globulin.

6. Involved in coagulation and anti coagulation Coagulation function

Most plasma Coagulation factor Physiological anticoagulant substances and substances promoting fibrinolysis are plasma proteins. Various coagulation factors and anticoagulant factors play an important role in reducing bleeding and preventing circulatory obstruction.

7. Physiological hemostatic function

albumin

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Physical and chemical properties

Human plasma albumin Albumin is the most abundant protein in human plasma, about 45g/L, accounting for Total protein 60%. The liver synthesizes 12g albumin every day, accounting for 50% of the liver secreted protein. Human plasma albumin gene Located at No. 4 chromosome First, its primary translation product is Prealbumin (preproalbumin）。 In the process of secretion, the signal peptide is cut off to generate proalbumin. And then Golgi Corpuscular meridian cathepsin B excises a 6-peptide fragment (Jing Gan Val Phenylpropyl Jing Jing) at the N-terminal to become mature albumin. A strip composed of 585 amino acids Polypeptide chain , containing 17 disulfide bonds, molecular weight About 69000. The molecule of albumin is elliptical, and its long and short axes are 150? And 38?, Compared with globulin and fibrinogen molecules, albumin has lower viscosity. The isoelectric point of albumin is pH4.7, which is lower than the PI of other components of plasma protein. Therefore, the PI of albumin is lower than that of other components of plasma protein Electrophoresis buffer With many negative charges and small molecular weight, electrophoretic migration is fast^[1] 。

physiological function

Plasma albumin has two main physiological functions:

① Maintain plasma colloid osmotic pressure. Because albumin content in plasma is the highest and its molecular weight is small, its molecular number in plasma is the largest. Therefore, it plays a major role in plasma colloid osmotic pressure, providing 75-80% of plasma total colloid osmotic pressure.

② It can be combined with various ligands for transportation. Many substances such as free fatty acids 、 bilirubin 、 sex hormone 、 thyroxine 、 adrenaline , metal ions Sulfonamides 、 Penicillin G 、 Dicoumarin 、 aspirin And other drugs can combine with albumin to increase Hydrophilicity It is convenient for transportation.

Metal bonding

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Haptoglobin

Is a kind of Plasma glycoprotein , the molecular weight is about 90.000. Can and red blood cell Outside hemoglobin (Hb) combines to form a compact non covalent complex Hb Hp. Each 100ml of plasma is enough to combine 40? Hp of 80mg hemoglobin. About 10% of the Hb degraded every day is released into the blood circulation, becoming the free Hb outside the red blood cells. The molecular weight of Hb Hp complex formed by Hb and Hp can reach 155.000, which cannot be penetrated glomerulus To prevent Free hemoglobin Loss from kidney to avoid the loss of iron contained in Hb. Ensure that iron is reused for anabolism.

Hemolytic anemia Patient plasma Haptoglobin The concentration drops. As a large amount of Hb is released during hemolysis, Hp and free Hb are combined into a complex and absorbed and cleared by liver cells. In addition, Hp is also an acute phase protein, and its plasma content increases when suffering from various inflammation.

Iron transporter

Iron transporter belongs to beta globulin. It is a glycoprotein synthesized in the liver, with a molecular weight of about 80.000. With high polymorphism, more than 20 different types of Tf have been found. Each molecule of Tf can bind 2 molecules of Fe3+. The physiological function of iron transporters is to transport iron to tissues and cells that need iron. Hemoglobin is catabolized every day, releasing about 25mg of iron. Free iron is toxic. When combined with Tf, it not only reduces the toxicity but also transports the iron to the iron demanding part.

Iron is a lot Ferritin biological activity It is essential for the play of, such as hemoglobin, myoglobin Cytochrome , peroxidase, etc. Therefore, any growth Proliferating cell There are receptors for iron transporters on the membrane of. The Tf carrying Fe3+binds to the receptor and enters the cell through endocytosis for intracellular synthesis and utilization.

Test sheet

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The liver is the main organ of protein metabolism. For example, albumin, lipoproteins, coagulation factors, fibrinolytic factors and various transport proteins are synthesized by hepatocytes, and these proteins will decrease when liver function is damaged; Although gamma globulin is not synthesized by liver cells, it can increase when liver function is damaged, such as inflammation. Determination of plasma protein level can understand the metabolic function of liver to protein.

The most common abnormal change of fatty liver is the change of total plasma protein and the inversion of the ratio of albumin to globulin. Some patients' plasma protein electrophoresis shows that α 1 -, α 2 -, and β - globulin increase. After the cure of fatty liver, the abnormality of plasma protein recovers later than any other biochemical changes, and it usually takes 3-6 months before it returns to normal.^[2]

application

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Pig blood is widely used in feed industry, food industry and pharmaceutical industry in China.

(1) Application in feed

Blood feed for livestock and poultry was mainly used in the form of boiled or pressed blood meal before the 1980s. In the early 1980s, some scientific research units and enterprises began to jointly develop fermented blood meal. For example, Wuhan Meat Factory is the same as Wuhan Institute of Virology, Chinese Academy of Sciences , "Feed Zhuang - W Fermented Blood Meal"; In the mid-1980s, Hangzhou Business School successfully trial produced enzymatic pig blood powder^[3] 。

(2) Application in food industry.

① In meat products: add proper amount of pig plasma protein in sausage, sausage, western style ham and meat jerky, the fat content is slightly reduced, the protein content is improved, especially the plasma protein emulsification performance is good, the water retention, slicing, elasticity, particle size and yield of the product are improved, and the cost is reduced. For example, when the processing plant of Taixian Food Company in Jiangsu Province added 10% - 12% plasma to sausage, the protein content increased by 7%, the product yield increased by 20.4%, and the cost per kilogram of sausage decreased by 5% - 8%. The plant added blood powder instead of eggs to preserved meat, which had a good effect and saved costs.

② Cooking dishes: Tianjin Meat Federation Plant uses pig plasma protein to cook 12 kinds of dishes, such as fried diced protein, pan other protein, spicy oil protein, four protein treasures, etc. These dishes have the characteristics of high protein and low fat. They are delicious, smooth and delicious. They are not greasy when eaten. They are rich in nutrition, good in color, smell and taste.

③ Confectionery: After plasma or whole blood is hydrolyzed, its protein content is higher than that of milk powder. Handan Meat Joint Factory has developed edible protein through enzyme degradation, decolorization and deodorization, which has a good effect on application and pastry. Yangzhou Biochemical Pharmaceutical Factory adopts enzymatic hydrolysis of blood protein powder, adding Jingguo powder, cake, biscuit, bread, etc. in the proportion of 1%, 2%, 3%, and the effect is also very good. Shanghai food graduate students mixed blood protein powder into bread and biscuits to increase the protein content of the product. It is found through application Plasma protein powder It is a good foaming agent and emulsifier. Jiangsu Taizhou Meat Joint Factory added plasma protein to the cake, which can partially replace eggs, and the effect is very good^[4] 。

④ Nutritional supplement: because the blood contains rich protein, trace elements and iron, it is especially suitable for nutritional additives.

(3) Application in pharmaceutical industry

① Hematoporphyrin derivatives: Hematoporphyrin derivatives are worth the molecular structure modification on the basis of protoporphyrin. This substance is associated with Ribonucleic acid The function of close combination. Yangzhou Biochemical Pharmaceutical Factory has undertaken the national key research project "Laser Hematoporphyrin Derivatives for Cancer Prevention" basal cell carcinoma , melanin cancer, gastric cancer, esophageal cancer and other clinical trials have a strong killing power on cancer cells, and the drug toxicity is small. The curative effect is good.

② Protoporphyrin sodium: The protoporphyrin sodium developed by Yangzhou Biochemical Pharmaceutical Factory by esterification method has the effect of protecting liver and reducing transaminase, and is used for treatment Acute and chronic hepatitis 。

③ Superoxide dismutase (SOD): SOD is an enzyme which is made from pig blood by biochemical method and has an important protective effect. It can effectively remove superoxide radical anions. China's Suzhou Medical College and Suzhou Biochemical Pharmaceutical Factory have jointly developed it, and a technology development company in Zhuhai has also successfully developed it.

④ Globulin preparation: Hangzhou Business School prepares globulin preparation from pig blood, which is mainly used in veterinary medicine. In addition, we have extracted some substances from the blood, such as hematolysin, oxidized heme, amino acid, thrombin, immune serum, etc., which are used in the pharmaceutical industry^[5] 。

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