catalysis

Enzymes are a type of biological catalysts that govern many catalytic processes such as metabolism, nutrition, and energy conversion of organisms. Most of the reactions closely related to life processes are enzyme-catalyzed reactions.

These properties of enzymes enable the intricate substance metabolism processes in cells to proceed in an orderly manner, allowing substance metabolism to adapt to normal physiological functions. If an enzyme is defective due to genetic defects, or the activity of the enzyme is weakened due to other reasons, it can lead to abnormal reactions catalyzed by the enzyme, disordered substance metabolism, and even disease. Therefore, enzymes are closely related to medicine.

Enzymes allow the body to digest and absorb the food it eats, and maintain all functions of the internal organs, including cell repair, metabolism, immunity improvement, energy production, and blood circulation. For example, when rice is chewed in the mouth, the longer the chewing time, the more obvious the sweetness. This is because the starch in the rice is hydrolyzed into maltose under the action of salivary amylase secreted by the mouth. Therefore, chewing more when eating can fully mix food with saliva, which is beneficial to digestion. In addition, there are various hydrolytic enzymes such as pepsin and trypsin in the human body. The protein that the human body absorbs from food must be hydrolyzed into amino acids under the action of pepsin and other enzymes. Then, under the action of other enzymes, more than 20 amino acids needed by the human body are selected and recombined into the amino acids needed by the human body in a certain order. Various proteins.

Catalytic mechanism

The catalytic mechanism of enzymes is basically the same as that of general chemical catalysts. It is first combined with the reactants (enzyme substrates) to form a complex, and the speed of the chemical reaction is increased by reducing the activation energy of the reaction. At a constant temperature, in the chemical reaction system Although the energy contained in each reactant molecule varies greatly, its average value is low. This is the initial state of the reaction.

The reaction of S (substrate) → P (product) can proceed because a considerable part of S molecules have become activated (transition state) molecules. The more activated molecules, the faster the reaction speed. At a specific temperature, the activation energy of a chemical reaction is the energy (kilocalories) required to turn all the molecules of 1 mole of a substance into activated molecules.

The function of enzyme (E) is to temporarily combine with S to form a new compound ES. The activation state (transition state) of ES contains much lower energy than the activated molecules of the reactants in the chemical reaction without a catalyst. ES reacts again to produce P and releases E at the same time. E can combine with another S molecule, and the cycle repeats. Reduce the activation energy required for the entire reaction, allowing more molecules to react per unit time and speeding up the reaction. If there is no catalyst, the reaction of decomposing hydrogen peroxide into water and oxygen (2H2O2→2H2O+O2) requires an activation energy of 18 kcal per mole (1 kcal = 4.187 Joules). Catalase is used to catalyze this reaction. When , only 2 kcal of activation energy per mole is required, and the reaction speed increases approximately 1011 times.

Enzyme (E) and substrate (S) form an enzyme-substrate complex (ES)

The directional binding of the active center of the enzyme to the substrate to form an ES complex is the first step in enzyme catalysis. The energy of directional binding comes from various non-covalent bonds formed when the enzyme active center functional group interacts with the substrate, such as ionic bonds, hydrogen bonds, hydrophobic bonds, and van der Waals forces. The energy produced when they combine is called binding energy energy). It is not difficult to understand that each enzyme has selectivity in binding to its own substrate.

If the enzyme only complements the substrate to form an ES complex and cannot further promote the substrate to enter the transition state, the catalytic effect of the enzyme cannot occur. This is because after the enzyme and the substrate form an ES complex, more non-covalent bonds must be formed between the enzyme and the substrate molecules to form a complex that complements the transition state of the enzyme and the substrate in order to complete the catalytic effect of the enzyme. In fact, in the process of generating more non-covalent bonds, the substrate molecules are transformed from the original ground state to the transition state. That is, the substrate molecules become activated molecules, which provide conditions for the combination and arrangement of groups required for the substrate molecules to undergo chemical reactions, the generation of instantaneous unstable charges, and other transformations. Therefore, the transition state is not a stable chemical substance, unlike the intermediate product in the reaction process. As far as the transition state of a molecule is concerned, the probability of it transforming into a product (P) or a substrate (S) is equal.

When the enzyme and substrate form an ES complex and further form a transition state, this process has released more binding energy. It is now known that this part of the binding energy can offset the activation energy required for the activation of some reactant molecules, so that molecules that were originally below the activation energy threshold can also become activated molecules, thereby accelerating the speed of the chemical reaction.

Both enzymes and general catalysts speed up chemical reactions by reducing the activation energy of the reaction.

Catalytic specificity of enzymes In terms of its substrate selectivity and specificity of catalytic reactions. Except for some spontaneous chemical reactions in the body, most of them are catalyzed by specific enzymes. An enzyme can find its substrate from thousands of reactants. This is the specificity of the enzyme. According to the difference in the degree of specificity of enzyme catalysis, it is divided into specificity (absolute specificity), relative specificity There are three types of enzymes: stereospecificity and stereoisomer specificity. An enzyme that catalyzes only one substrate is called specific, such as urease, which can only hydrolyze urea into carbon dioxide and ammonia. If an enzyme can catalyze a class of compounds or a class of chemical bonds, it is called relative specificity, such as esterase, which can catalyze the hydrolysis of triglycerides and other ester bonds. Enzymes with stereoisomer specificity have strict requirements on the stereo configuration of substrate molecules, such as L-lactate dehydrogenase, which only catalyzes the dehydrogenation of L-lactic acid and has no effect on D-lactic acid.

The catalytic activity of some enzymes can be affected by many factors, such as allosteric enzymes being regulated by allosteric agents, some enzymes being regulated by covalent modifications, neurohumoral regulation of enzyme activity through second messengers, and inducers or inhibitors regulating intracellular enzyme content (changing the rate of enzyme synthesis and decomposition).

It should be pointed out that the catalytic reaction of an enzyme is often the combined effect of multiple catalytic mechanisms, which is an important reason for the high efficiency of enzyme-promoted reactions.

application

Disease diagnosis

With the in-depth study and increasing understanding of enzymes, complex enzymes rich in high-concentration SOD have played an increasingly important role in the treatment of diseases. The activity of enzymes in normal human bodies is relatively stable. When certain tissues of the human body are damaged or diseases occur, certain enzymes are released into the blood, urine or body fluids. For example, in acute pancreatitis, the activity of amylase in serum and urine increases; in hepatitis and other causes of liver damage, liver cell necrosis or increased permeability, a large amount of transaminase is released into the blood, causing serum transaminase to increase; in myocardial infarction, serum lactate dehydrogenase and creatine phosphokinase increase significantly. When poisoned by organophosphorus pesticides, cholinesterase activity is inhibited and serum cholinesterase activity decreases; in certain hepatobiliary diseases, especially bile duct obstruction, serum r-glutamyl transferase increases, and so on. Therefore, with the help of enzyme activity determination in blood, urine or body fluids, the occurrence and development of certain diseases can be understood or determined.

Clinical Governance

Enzyme therapy has gradually been recognized by people, and various enzyme preparations are increasingly widely used in clinical practice. For example, trypsin and chymotrypsin can catalyze protein decomposition. This principle has been used in surgical wound expansion, purification of suppurative wounds, and treatment of chest and abdominal serosal adhesions. In the treatment of thrombophlebitis, myocardial infarction, pulmonary infarction, and disseminated intravascular coagulation, plasmin, streptokinase, urokinase, etc. can be used to dissolve blood clots and prevent the formation of thrombi.

Some compound natural enzymes, with high-unit SOD enzyme as the main formula, can not only be used for auxiliary treatment of important organs such as the brain, heart, liver, and kidney. In addition, the principle of competitive inhibition of enzymes is also used to synthesize some chemical drugs for antibacterial and bactericidal treatment. For example, enzyme spleen tonic also has a good conditioning effect on problems such as infertility. Sulfonamides and many enzymes that can inhibit the growth of certain bacteria have antibacterial and bactericidal effects; many drugs can inhibit enzymes related to nucleic acid or protein synthesis in cells, thereby inhibiting the differentiation and proliferation of tumor cells; thiouracil can inhibit iodine, thereby affecting the synthesis of thyroid hormone, so it can be used to treat hyperthyroidism, etc.

Production and living

The yeast used in the brewing industry is produced by related microorganisms. The enzyme converts starch and other substances into alcohol through hydrolysis and oxidation. The production of soy sauce and vinegar is also completed under the action of enzymes. The nutritional value of feed treated with amylase and cellulase is improved. Adding enzymes to washing powder can improve the efficiency of washing powder and make it easy to remove sweat stains that were originally difficult to remove, etc.

Due to the wide application of enzymes, the extraction and synthesis of enzymes have become important research topics. At this time, enzymes can be extracted from organisms, such as bromelain from pineapple peel. However, since the content of enzymes in organisms is very low, a large number of enzymes in industry are produced by fermentation of microorganisms. Generally, it is necessary to select and breed the required strains under suitable conditions, let them reproduce, and obtain a large number of enzyme preparations. In addition, people are studying the artificial synthesis of enzymes. In short, with the improvement of scientific level, the application of enzymes will have a very broad prospect.