What are Proteolytic Enzymes?

Protease, proteinase is a collective name for enzymes that catalyze the hydrolysis of polypeptides or proteins, referred to as proteases. Widely divided into animals, plants and bacteria, there are many types, and the lysozyme content of various cells in the animal's digestive tract and body is particularly rich. Proteases play an important role in the body's metabolism and biological regulation. The molecular weight is generally around 20,000-30,000. Proteases can be divided into endopeptidases and exopeptidases according to the site of hydrolysis of the substrate. The former hydrolyzes the peptide bonds in the middle part of the protein, and the latter degrades amino acid residues from the amino or carboxyl terminus of the protein. ^[1]

Chinese name: Proteolytic enzyme
Foreign name: protease, proteinase

Definition: A collective term for enzymes that catalyze the hydrolysis of peptides or proteins
Distribution: Among animals, plants and bacteria

Classification of proteolytic enzyme properties

It can be divided into four categories according to the properties of various protease active sites:

Proteolytic enzyme serine protease

In addition to serine, its active center includes histidine and aspartic acid residues, such as various endopeptidases secreted by the pancreas and various proteases related to coagulation, hemolytic fibers, and the complement system.

Proteolytic enzyme thiol protease

Its active center requires histidine residues in addition to cysteine, such as plant-derived and cytolytic enzymes

Proteolytic enzyme method Certain cathepsins in the body.

Proteolytic enzyme aspartic protease

Their active centers are composed of two aspartic acid residues, such as pepsin secreted by the gastric membrane, angiotensin-releasing enzyme in the kidney, and some cathepsins in the lysosome.

Proteolytic metalloproteinases

Its active center requires other amino acid residues besides metal ions. For example, the active center of pancreatic carboxypeptidase A includes zinc ion (Zn2 +) and glutamic acid and tyrosine residues. Most exopeptidases and certain bacterial proteases often fall into this category.

In addition to the groups that participate in the catalytic peptide bond hydrolysis, various proteases also need to have certain sites that bind to the substrate. Because of these different sites, different specificities of various proteases are determined. ^[1]

Proteolytic enzyme functional classification

After discovering the important role of proteases in biological regulation, they can be classified according to their physiological functions and specificity.

Proteolytic enzyme

It means that the specificity of the enzyme is very poor, and it can hydrolyze very peptide bonds in the protein, so that various small peptides and even free amino acids can be generated. The physiological functions of these proteases are mainly involved in the degradation of proteins in the body. For example, various proteases secreted by the gastrointestinal system digest and decompose food proteins in vitro; various cathepsins in the body can clear various metabolisms in the body. product. Red blood cells with an average lifespan of 120 days, their hemoglobin is degraded by cathepsin.

Proteolytic enzymes

It means that the specificity of the enzyme is very strong, it only acts on a specific protein substrate, hydrolyzes specific peptide bonds therein, and then produces various active polypeptides or proteins with different physiological functions. These proteases play a biological regulatory role in the body. Most of them belong to serine proteases, which are similar to trypsin in terms of specificity, that is, they only act on peptide bonds formed by the carboxyl terminus of arginine or lysine. These proteases are different from ordinary proteases, and have low or no effect on the degradation of common proteins such as casein or hemoglobin. Even the protein substrates that are specifically hydrolyzed have strict requirements on the conformation. Once the substrate is denatured, Proteases that cannot be degraded by it, but not restricted hydrolysis, do the opposite. The greater the degree of denaturation of the protein substrate, the easier it is to hydrolyze. For example, when thrombin activates fibrinogen, the peptide bonds of 150 arginine or lysine residues only hydrolyze the sperm-glycine bonds near the N-terminus of fibrinogen and subunits to release bleeding. Fibrin A, B, so that soluble fibrinogen is transformed into gel network fibrin. ^[1]

Regulation of proteolytic enzymes

Many important physiological effects in the body are related to the biological regulation of proteases. As listed in the table, when the body is exposed to external stimuli and responds to the corresponding physiological reactions, the proteases in the body are mobilized to make certain polypeptides or proteins that had no physiological activity quickly become functions. Strong corresponding products, so as to achieve the purpose of defense, survival and reproduction of the body. Some mobilization processes are relatively simple and can be accomplished through a catalytic reaction. For example, inactive trypsinogen in the gastrointestinal tract produces active trypsin when its N-terminus is hydrolyzed by enterokinase to remove a 6 peptide. Some processes are quite complicated and require multiple catalytic reactions, such as blood coagulation and complement reactions, which involve more than 10 components.

Proteolytic enzyme action characteristics

Proteolytic enzyme biological effects are transient

Activity is rapidly shown by activation of active protein precursors in the body. Because there is no need for complicated processes such as gene replication, transcription and expression, it can quickly respond to external signals. In addition, this response is directional and irreversible, different from the biological regulation mechanisms of other enzymes in the body, such as some phosphorylated kinases, through the phosphorylation and dephosphorylation of proteins to produce allosteric effects, thereby performing reversible biological regulation. .

Proteolytic enzymes are expressed in a cascade

That is, the protein that is activated in the first-stage reaction is itself a protease that catalyzes the next-stage reaction, so it plays the role of step-up amplification. Example 2: For example, even if a molecule of enzyme catalyzes the reaction of 1000 molecular substrates at a very low level, it will be amplified by 1 million times after two-stage catalytic reaction, so the body can have a strong biological effect on weak external signals.

Positive and negative feedback system

Therefore, the entire multi-stage reaction system is in an optimal state. For example, thrombin that is activated during the blood coagulation process is not only

Proteolytic enzymes ^[2] It can catalyze the conversion of fibrinogen to fibrin, and it can also activate coagulation factors and , which further promotes the activation of thrombin. This is a positive feedback, but thrombin can degrade thrombin by itself, so that It can no longer be activated, this is negative feedback.

When catalyzing the same active protein precursor, sometimes two or more components with different biological functions, such as adrenergic hormone, -lipotropin, and endorphin, are produced from the same precursor protein.

Proteases involved in biological regulation can sometimes produce the same physiological effect through two different pathways, which play a complementary role to each other. For example, both the endogenous activation system in the blood and the exogenous activation system in the tissue are involved in the coagulation reaction, and both of them finally activate prothrombin through factor X.

Protease inhibitors exist almost without exception in some important biological regulatory systems involved in proteases. If the balance between the protease and its corresponding inhibitor is imbalanced in some systems, it can cause disease. For example, congenital venous thrombosis and vascular neuroedema are often related to the lack of corresponding antithrombin inhibitor III and complement C1 inhibitors in the body.

Application of proteolytic enzymes

Due to the rich sources of protease, in addition to extracting from animals and plants, it can also be produced by a large amount of bacteria. It has been widely used in medical, food, tanning, reeling and other industries, and can also be used as an important biochemical reagent. For example, chymotrypsin is used in cataract extraction surgery, which simplifies the operation and improves the success rate; trypsin has a significant effect on removing necrotic tissue, anti-inflammatory and purulent, and healing wounds; urokinase and streptokinase are used to treat venous thrombosis and vasculitis; Kallikrein is used to improve coronary heart disease, relax microvessels, and lower blood pressure; elastase has a certain effect on vascular sclerosis; bacterial protease is used for leather depilation and silk gum. Rennet is used to make cheese products; papaya or bromelain is used as a beer stabilizer, which can eliminate protein precipitation caused by cold storage of beer.