Proteinase

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Protease is a general term for a class of enzymes that hydrolyze protein peptide chains. According to the way it degrades polypeptides, it is divided into endopeptidase and telopeptase. The former can cut the large molecular weight polypeptide chain from the middle to form smaller molecular weight prions and peptones; the latter can be divided into carboxypeptidase and aminopeptidase, which separate peptides from the free carboxyl end or free amino end of the polypeptide one by one.

Figure 1. Protein structure of protease.

Classification

The general term for a class of enzymes that hydrolyze protein peptide bonds. According to the way they hydrolyze polypeptides, they can be divided into endopeptidases and exopeptidases. Endopeptidase cuts the inside of protein molecules to form smaller molecular weights and peptones. Exopeptidase hydrolyzes peptide bonds from the free amino or carboxyl ends of protein molecules one by one, and frees amino acids. The former is aminopeptidase and the latter is carboxypeptidase. According to its active center and optimal pH value, proteases can be divided into serine proteases, sulfhydryl proteases, metalloproteases and aspartic proteases. According to the optimal pH value of the reaction, it is divided into acid protease, neutral protease and alkaline protease. Proteases used in industrial production, mainly endopeptidases.

Specificity

Proteolysis may be highly confounded, so that multiple protein substrates are hydrolyzed. This is the case for digestive enzymes such as trypsin, which must be able to cleave protein arrays that take in smaller peptide fragments. Promiscuous proteases usually bind to a single amino acid on the substrate and therefore only have specificity for that residue.

Functions of trypsin

The role of trypsin is to hydrolyze the protein between cells to separate the cells. Different tissues or cells react differently to the action of pancreatin. The activity of pancreatin dispersed cells is also related to its concentration, temperature and action time. When the pH is 8.0 and the temperature is 37°C, the pancreatin solution has the strongest effect. When using pancreatin, the concentration, temperature and time should be controlled to avoid cell damage caused by over-digestion.

Applications

Protease is one of the most important industrial enzyme preparations, which can catalyze the hydrolysis of proteins and polypeptides and is widely found in animal organs, plant stems and leaves, fruits and microorganisms. Proteases are used in large quantities in cheese production, meat tenderization and vegetable protein modification. In addition, pepsin, chymotrypsin, carboxypeptidase, and aminopeptidase are all proteases in the human digestive tract. Under their action, the protein ingested by the human body is hydrolyzed into small peptides and amino acids. The proteases currently used in the bakery industry include mold proteases, bacterial proteases and plant proteases. The application of protease in bread production can change the properties of gluten, and its form of action is different from the effect of force during bread preparation and the chemical reaction of reducing agents. The role of protease is not to break the disulfide bonds, but to break the three-dimensional network structure of gluten. The role of protease in bread production is mainly manifested in the dough fermentation process.

Inhibitors

The activity of proteases is inhibited by protease inhibitors. One of protease inhibitors is the serpin superfamily. It includes alpha 1-antitrypsin (which protects the body from excessive effects of its own inflammatory proteases), alpha 1-antichymotrypsin (which does likewise), C1-inhibitor (which protects the body from excessive protease-triggered activation of its own complement system), antithrombin (which protects the body from excessive coagulation), plasminogen activator inhibitor-1 (which protects the body from inadequate coagulation by blocking protease-triggered fibrinolysis), and neuroserpin.

Figure 2. Natural protease inhibitor, lipocalin protein family.