An enzyme is a protein or RNA produced by living cells that are highly specific and highly catalytic for its substrate. The catalysis of the enzymes depends on the integrity of the primary structure and spatial structure of the enzyme molecule.
Degeneration of the enzyme molecule or depolymerization of the subunit can result in loss of enzyme activity. Enzymes are biological macromolecules with a molecular mass of at least 10,000 and a large number of up to one million.
Enzymes are a very important class of biocatalysts. Due to the action of the enzyme, the chemical reaction in the living body can be carried out efficiently and specifically under extremely mild conditions.
With the deepening and development of the research on the structure and function of enzyme molecules and the kinetics of the enzymatic reaction, the discipline of enzymology has gradually formed.
What are Enzymes Made of
The chemical nature of the enzyme is protein or RNA (Ribonucleic Acid), so it also has primary, secondary, tertiary, or even quaternary structure. According to their molecular composition, they can be divided into simple enzymes and binding enzymes.
A protein-only enzyme is called a simple enzyme. a binding enzyme is composed of an enzyme protein and a cofactor. For example, most hydrolases consist of proteins alone, flavin mononucleotides consist of enzyme proteins and cofactors. enzymes meaning
The enzyme protein in the binding enzyme is a protein part, and the cofactor is a non-protein part, and only the two are combined into a whole enzyme to have catalytic activity.
In 1833, France’s Payen and Persoz precipitated from the hydrolysate of malt with a substance that hydrolyzes starch to form sugar and named it diastase, which is now called Amylase. Later, diastase became the name used to represent all enzymes in France.
In 1836, T. Schwann (1810 – 1882), a scientist at the Max Planck Institute for Biology, extracted the protein from the gastric juice and solved the mystery of digestion.
In 1878, Kunne called the substance of alcohol fermentation in yeast called “Enzyme“, this time from Greek, meaning “in alcohol.”
In 1913, American scientists Michaelis and Menten derived the formula of the basic equation of enzyme catalysis based on the theory of intermediate products.
In 1926, US scientists Sumner (JBSumner, 1887-1955) is extracted from the seeds of beans crystallized urease, and by chemical experiments confirmed that urease is a kind of protein.
In the 1930s, scientists have extracted protein crystallization variety of enzymes and pointed out that the enzyme is a class of biocatalytic protein function.
In 1982, American scientists Petrech (TRCech, 1947- ) and Altman (S. Altman, 1939-) discovered that a small number of RNAs also have biocatalytic effects and named them ribozymes.
In 1982, American scientist T. Cech and his colleagues found that the RNA of the splicing intron itself has a catalytic function in the study of the DNA sequence containing the interstitial sequence of the tetracycline-encoding rRNA precursor. In order to distinguish it from the enzyme, Cech named it ribozyme, translated as “ribozyme”, which is also called “catalytic small RNA” in the classification of non-coding RNA.
In 1986, Schultz and Lerner developed abzymes.
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Enzyme Reaction Characteristics
1 High efficiency: The catalytic efficiency of the enzyme is higher than that of the inorganic catalyst so that the reaction rate is faster.
2 Specificity: an enzyme can only catalyze one or a type of substrate, such as proteases can only catalyze the hydrolysis of proteins into peptides.
3 Diversity: There are many kinds of enzymes, and about 4,000 kinds of enzymes have been found so far, and the enzymes in the organisms are much larger than this number.
4 Mildness: It means that the chemical reaction catalyzed by the enzyme is generally carried out under mild conditions.
5 Activity regulatable: including inhibitor and activator regulation, feedback inhibition regulation, covalent modification regulation, and allosteric regulation.
6 variability: Most enzymes are proteins, which are destroyed by high temperature, strong acid, strong alkali, etc.
7 The catalytic properties of some enzymes are related to cofactors.
8 changing the chemical reaction rate, which is almost not consumed by itself.
9 catalyzes only existing chemical reactions.
10 can speed up the chemical reaction, but the enzyme cannot change the equilibrium point of the chemical reaction, that is to say, the enzyme promotes the forward reaction and promotes the reverse reaction in the same proportion, so the effect of the enzyme is to shorten the need to reach equilibrium. Time, but the equilibrium constant is unchanged.
11 reduce the activation energy and accelerate the chemical reaction rate.
12 Like inorganic catalysts, poisoning can also occur.
Enzymes are a class of biocatalysts that govern many metabolic processes such as biological metabolism, nutrient, and energy conversion. Most of the reactions closely related to life processes are enzyme-catalyzed reactions.
These properties of the enzyme enable the intricate metabolism of substances in the cell to proceed in an orderly manner, allowing the metabolism of the substance to adapt to normal physiological functions.
If an enzyme deficiency is caused by genetic defects, or the activity of the enzyme is weakened by other reasons, the reaction catalyzed by the enzyme may be abnormal, the metabolism of the substance may be disordered, and even the disease may occur, so the relationship between the enzyme and the medicine is very close.
The enzyme digests and absorbs the food that the human body eats, and maintains all functions of the internal organs including cell repair, anti-inflammatory detoxification, and metabolism, improving immunity, generating energy, and promoting blood circulation.
For example, when the rice is chewed in the mouth, the longer the chewing time, the more obvious the sweetness is due to the hydrolysis of the starch in the rice to the maltose by the action of salivary amylase secreted by the mouth.
Therefore, chewing at the time of eating can fully mix the food with saliva, which is conducive to digestion. In addition, there are various hydrolase enzymes such as pepsin and trypsin in the human body.
The protein that the human body takes from food must be hydrolyzed into amino acids under the action of pepsin, and then, under the action of other enzymes, select more than 20 amino acids required by the human body, and recombine the adult body in a certain order. Various proteins.
The catalytic mechanism of the enzyme is basically the same as that of the general chemical catalyst. It is also combined with the reactant (substrate of the enzyme) to form a complex, which can increase the speed of the chemical reaction by reducing the energy of the reaction.
At a constant temperature, each chemical reaction system although the energy contained in the reactant molecules is quite different, the average value is lower, which is the initial state of the reaction.
S (substrate) → P (product) this reaction can be carried out because a considerable part of the S molecule has been activated to become an activated (transition state) molecule, and the more activated molecules, the faster the reaction rate.
At a particular temperature, the activation energy of a chemical reaction is the energy (kcal) required to make all molecules of a mole of material activating molecules.
The function of the enzyme (E) is to temporarily combine with S to form a new compound ES, and the activation state (transition state) of the ES is much lower than that of the reactant activation molecule in the chemical reaction without the catalyst. The ES re-reacts to produce P while releasing E.
E can be combined with another S molecule and this cycle is repeated. The activation energy required for the entire reaction is lowered so that more molecules are reacted per unit time, and the reaction rate is accelerated.
In the absence of a catalyst, the decomposition of hydrogen peroxide to water and oxygen (2H 2 O 2 →2H 2 O+O 2) requires activation energy of 18 kcal per mol (1 kcal = 4.187 joules). When the hydrogenase catalyzes this reaction, only the activation energy is required to be 2 kcal per mole, and the reaction rate is increased by about 10 11 times.
The enzyme (E) and substrate (S) form an enzyme-substrate complex (ES)
The active binding of the active center of the enzyme to the substrate to form the ES complex is the first step in the enzymatic action.
The energy of the directed binding comes from a variety of non-covalent bonds formed by the functional groups of the active center of the enzyme interacting with the substrate, such as ionic bonds, hydrogen bonds, hydrophobic bonds, and van der Waals forces.
Energy generated when they are called binding energy (binding energy). It is not difficult to understand that each enzyme is selective for the binding of its own substrate.
If the enzyme is only complementary to the substrate to form an ES complex, which does not further promote the substrate into a transition state, the catalytic action of the enzyme cannot occur.
This is because after the enzyme and the substrate generate the ES complex, it is necessary to form a more non-covalent bond between the enzyme and the substrate molecule to form a complex complementary to the transition state of the enzyme and the substrate, in order to complete the catalytic action of the enzyme.
In fact, in the process of generating more non-covalent bonds as described above, the substrate molecules are converted from the original ground state to a transition state. That is, the substrate molecule becomes an activating molecule, and conditions are provided for a combination arrangement of groups required for the chemical reaction of the substrate molecule, generation of an instantaneous unstable charge, and other transformation.
Therefore, the transition state is not a stable chemical, unlike the intermediate products in the reaction process. As far as the transition state of the molecule is concerned, the probability of its conversion to product (P) or conversion to the substrate (S) is equal.
When the enzyme forms an ES complex with the substrate and further forms a transition state, this process has released more binding energy. It is known that this part of the binding energy can offset the activation energy required for the activation of some of the reactant molecules, thereby making the original lower than the activation.
The energy threshold molecule also becomes an activating molecule, thus accelerating the rate of chemical reaction
Both enzymes and general catalysts accelerate the rate of chemical reactions by reducing the activation energy of the reaction.
The catalytic specificity of the enzyme is manifested in both its selectivity for the substrate and the specificity of the catalytic reaction. In addition to individual spontaneous reactions, most of the chemical reactions in the body are catalyzed by a specific enzyme. An enzyme can find its own substrate from thousands of reactants.
This is the specificity of the enzyme. The difference in the extent of enzymatic specificity, divided into absolute specific (absolute specificity), relatively specific (relative specificity) and stereoisomers specificity (stereospecificity) categories.
An enzyme that catalyzes only one substrate to react is absolutely specific. For example, urease can only hydrolyze urea to decompose it into carbon dioxide and ammonia.
If an enzyme can catalyze a compound or a type of chemical bond, it is called a relative. Specificity, such as esterase, can both catalyze the hydrolysis of triglycerides and hydrolyze other ester bonds.
Enzymes with stereospecificity have strict requirements on the stereo configuration of the substrate molecule. For example, L-lactate dehydrogenase 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 the regulation of allosteric enzymes by allosteric agents, the regulation of covalent modifications by some enzymes, the regulation of enzyme activity by hormones and neurohumoral fluids by second messengers, and the inducers.
Or the regulation of intracellular enzyme content (changing the rate of enzyme synthesis and decomposition) by the inhibitor.
It should be noted that the catalytic reaction of an enzyme is often a combination of various catalytic mechanisms, which is an important reason for the high efficiency of the enzyme to promote the reaction.
Properties of Enzymes
With the in-depth study of enzymes and more and more understanding, complex enzymes rich in high-concentration SOD have played an increasingly significant role in the conditioning of diseases.
In normal people, the enzyme activity is relatively stable. When certain organs and tissues of the human body are damaged or diseases occur, some enzymes are released into blood, urine or body fluids. In acute pancreatitis, amylase activity in serum and urine is significantly increased, hepatitis and other causes of liver damage, hepatocyte necrosis or permeability enhancement, a large amount of transaminase released into the blood, so that serum transaminase is elevated; when myocardial infarction, Serum lactate dehydrogenase, and phosphocreatine kinase were significantly elevated.
When organophosphorus pesticides are poisoned, cholinesterase activity is inhibited and serum cholinesterase activity is decreased; in certain hepatobiliary diseases, especially biliary obstruction, serum r-glutamyltransferase is increased.
Therefore, the occurrence and development of certain diseases can be understood or determined by measuring the activity of enzymes in blood, urine or body fluids.
Enzyme therapy has gradually been recognized, and the application of various enzyme preparations in clinical practice is becoming more and more common. Such as trypsin, chymotrypsin, etc., can catalyze the decomposition of proteins, this principle has been used for surgical expansion, suppurative wound purification, and treatment of thoracic and intraperitoneal serosal adhesions.
In the treatment of thrombophlebitis, myocardial infarction, pulmonary infarction, and disseminated intravascular coagulation, plasmin, streptokinase, and urokinase can be used to dissolve blood clots and prevent the formation of blood clots.
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Some compound natural enzymes, with high-unit SOD enzyme as the main formula, can be used not only for the adjuvant treatment of important organs such as brain, heart, liver, and kidney but also have significant effects in the use of tumors. In addition, the use of the principle of competitive inhibition of enzymes, the synthesis of some chemical drugs, antibacterial, bactericidal and anti-tumor treatment.
Such as enzymes tonic spleen and kidney in infertility and other issues, there are better conditioning. Sulfonamides and many antibiotics can inhibit the growth of certain bacteria, so they have antibacterial and bactericidal effects; many anti-tumor drugs can inhibit enzymes related to a nucleic acid or protein synthesis in cells, thereby inhibiting tumor cells. Differentiation and proliferation against tumor growth; thiouracil inhibit iodide enzymes, thus affecting the thyroid hormone synthesis, it is useful for treating hyperthyroidism.
Production and living
The yeast used in the wine industry is produced by related microorganisms. The action of enzymes passes starch, etc. through hydrolysis, oxidation, and other processes, and finally into alcohol; the production of soy sauce and vinegar is also carried out under the action of enzymes; amylase and cellulase treated feed, increased nutritional value; detergent enzyme is added to, detergent efficiency can be made.
Due to the wide application of enzymes, the extraction and synthesis of enzymes have become an important research topic. At this time, the enzyme may be extracted from a living body, such as from pineapple may extract the bromelain.
However, since the enzyme is contained in a low amount in the living body, a large number of industrial enzymes are obtained by fermentation of microorganisms. It is generally necessary to select the desired strain under suitable conditions, allow it to be propagated, and obtain a large amount of enzyme preparation.
In addition, people are studying the artificial synthesis of enzymes. In short, with the improvement of the scientific level, the application of enzymes will have a very broad prospect.
The relationship between enzymes and certain diseases
The diseases caused by enzyme deficiency are mostly congenital or hereditary. For example, albino is caused by tyrosine hydroxylase deficiency, and folate disease or primaquine-sensitive patients are deficient in 6-phosphate glucose dehydrogenase.
Many toxic diseases are caused almost by the inhibition of certain enzymes. When commonly used organophosphorus pesticides (such as trichlorfon, dichlorvos, 1059, and dimethoate) are poisoned, they are inactivated by their binding to an -OH on the serine of the essential group of the cholinesterase active center.
Cholinesterase can catalyze Acetylcholine is hydrolyzed to acetate and choline, when cholinesterase is suppressed inactivation, acetylcholine hydrolysis inhibited, causing push acetylcholine product, a series of symptoms such as muscle tremors, restlessness, Excessive sweating, slow heartbeat, etc.
Some metal ions because human poisoning because the metal ions (such as Hg 2+) can bind to the essential groups of some enzyme active centers (such as cysteine -SH) to inactivate the enzyme.
The human body and mammals contain at least 5,000 enzymes. They are either dissolved in the cytoplasm, either in combination with various membrane structures or at specific locations in other structures within the cell and are only activated when needed. These enzymes are collectively referred to as intracellular enzymes.
There are some enzymes that are secreted outside the cell after synthesis in the cell-extracellular enzymes.
By reaction nature
According to the nature of the reaction catalyzed by the enzyme, the enzymes are divided into six categories:
Oxidoreductases (oxidoreductase) substrate to promote the oxidation-reduction reaction of enzymes, a class of enzyme-catalyzed redox reaction, reductase, oxidase, and can be divided into two categories.
Transferases catalyze enzymes that transfer or exchange between certain groups (such as acetyl, methyl, amino, phosphate, etc.) between substrates. For example, methyltransferase, aminotransferase, acetyltransferase, transsulfase, kinase and polymerase, and the like.
Hydrolases are enzymes that catalyze the hydrolysis of substrates. For example, amylase, protease, lipase, phosphatase, glycosidase, and the like.
Lyases catalyze enzymes that remove a group from a substrate (non-hydrolyzed) and leave a double bond or a reverse reaction. For example, dehydratase, decarboxylase, carbonic anhydrase, aldolase, citrate synthase, and the like. Many lyases catalyze a reverse reaction that creates a new chemical bond between the two substrates and eliminates the double bond of a substrate. Synthase belongs to this class.
Isomerases are enzymes that catalyze the conversion of various isomers, geometric isomers or optical isomers. For example, isomerase, surface enzyme, racemase, and the like.
A ligase catalyzes the synthesis of a two-molecular substrate into a single molecule of a compound that is coupled with phosphate-cleaved release energy of ATP. For example, glutamine synthetase, DNA ligase, amino acid: tRNA ligase, biotin-dependent carboxylase, and the like.
According to the principle of uniform classification of enzymes published by the International Biochemical Association, on the basis of the above six categories, in each of the major types of enzymes, according to the characteristics of the groups or bonds acting on the substrate, it is divided into several sub-categories; Precisely indicating the nature of the substrate or reactant, each subclass is subdivided into several groups (sub-subclasses); each group contains several enzymes directly.
For example, lactate dehydrogenase (EC 220.127.116.11) catalyzes the following reactions:
By chemical composition
An enzyme belonging to a simple protein, other than protein, does not contain other substances such as urease, protease, amylase, lipase, ribonuclease, etc.
The enzymes belonging to the conjugated protein, in addition to the protein, also incorporate some thermostable non-protein small molecular substances or metal ions, the former is called decoenzyme, the latter is called cofactor, the combination of decoenzyme and cofactor The complex formed is called the holoenzyme, ie, the whole enzyme = decoenzyme + cofactor.
Some enzymes, such as various proteases in the digestive system, are synthesized and secreted as inactive precursors, and then delivered to specific sites. When needed in the body, they are converted into active enzymes by the action of specific proteolytic enzymes. effect.
The precursor of these non-catalytically active enzymes is called the zymogen. The pepsinogen (pepsinogen), trypsinogen (trypsinogen) and chymotrypsinogen (chymotrypsinogen) and the like. The process by which a substance acts on a zymogen to convert it into an active enzyme is called zymogen and activation of the zymogen.
A substance that converts an inactive zymogen into an active enzyme is called activin. Activin has a certain specificity for the activation of the zymogen.
For example, the chymotrypsin synthesized by pancreatic cells is a single peptide chain consisting of 245 amino acid residues, and there are 5 pairs of disulfide bonds in the molecule. The activation process of the zymogen is shown in Figure 4-3.
First, the peptide bond between the 15th arginine and the 16th isoleucine residue is hydrolyzed by trypsin to activate the fully catalytically active p-chymotrypsin, but the enzyme molecule is not yet stable, and the p-chymotrypsin itself Catalytic removal of the dimeric dipeptide into an α-chymotrypsin with a stable structure of a catalytically active well.
Under normal circumstances, most of the blood coagulation factors are basically in the form of the inactive zymogen. Only when the tissue or endothelium is damaged, the inactive zymogen can be converted into an active enzyme, triggering a series of enzymatic reaction cascade, eventually leading to a soluble fibrin original into stable fibrin polymer, recruit platelets formation of blood clots.
The essence of zymogen activation is to cut off specific peptide bonds in the zymogen molecule or to remove partial peptides, which is beneficial to the formation of zymogen activation in the active center of the enzyme. On the one hand, it ensures that the cells of the synthetase are not digested by proteases themselves.
Destruction, on the other hand, activates and exerts its physiological effects on specific physiological conditions and defined sites. After intimal damage such as tissue or activated coagulation factors; Stomach primary cell secretion of pepsinogen and pancreatic cells secreted chymotrypsinogen, trypsinogen, elastase original, respectively, to the corresponding active enzyme activation in the stomach and small intestine, promoting the digestion of food proteins is a clear example.
The zymogen activation caused by the cleavage of a specific peptide bond is widespread in the organism and is an important means of regulating the enzyme activity of the organism. If the zymogen activation process is abnormal, it will lead to a series of diseases.
Hemorrhagic pancreatitis is because protease original into the small intestine when not is activated, their proteolytic activation of pancreatic cells, the pancreas bleeding, swelling.
The concept of isoenzyme: isozyme is a class of enzymes that catalyze the same chemical reaction, but the molecular structure, physicochemical properties and immunogenicity of the enzyme protein are different.
They exist in the same race of the organism or in different tissues of the same individual, even in different organelles of the same tissue, the same cell.
There are dozens of isozymes known to date, such as hexokinase, lactate dehydrogenase, etc. Among them, Lactic acid dehydrogenase (LDH) is the best studied. In human and spinal animal tissues, there are five molecular forms that catalyze the same chemical reactions:
The five isozymes are composed of four subunits. The subunits of LDH are divided into skeletal muscle type (M type) and myocardial type (H type). The amino acid composition of the two types of subunits is different. The tetramers composed of two subunits in different proportions exist in five LDH forms. That is, H 4 (LDH1), H 3 M 1 (LDH 2 ), H 2 M 2 (LDH 3 ), H 1 M 3 (LDH 4), and M 4 (LDH 5 ).
The amino acid composition of the M and H subunits are different, which is determined by the difference in genes. The proportions of M and H subunits in the five LDHs vary, which determines the difference in their physical and chemical properties. Usually, the five kinds of LDH can be separated by the electric ice method.
The LDH1 moves to the positive electrode fastest, while the LDH 5 moves the slowest. The others are somewhere in between, followed by LDH2, LDH3, and LDH4. The amount of LDH contained in different tissues is different, and the amount of LDH1 and LDH2 is more in the myocardium, while LDH5 and LDH4 are mainly in skeletal muscle and liver.
The difference in LDH isozyme zymograms in different tissues is related to the physiological process of tissue utilization of lactic acid. LDH1 and LDH2 have a large affinity for lactic acid, and dehydro-oxidize lactic acid to pyruvic acid, which is beneficial to the energy of the heart muscle from lactic acid oxidation.
LDH5 and LDH4 have a high affinity for pyruvic acid and have the effect of reducing pyruvate to lactic acid, which is compatible with the physiological process by which muscles gain energy in anaerobic glycolysis.
These isozymes are released into the blood during tissue lesions and the serum isozyme spectrum changes due to the distribution of isozymes in tissues and organs. Therefore, serum isoenzyme analysis is commonly used in the clinical diagnosis of diseases.
Allosteric enzymes are often oligomeric enzymes with a quaternary structure of multiple subunits. Except for catalytically active centers in the enzyme molecule, also called catalytic sites; there are also allosteric sites (Allosteric site). The latter is the position of the allosteric effector.
When it is combined with the allosteric agent, the molecular conformation of the enzyme changes slightly, affecting the affinity of the catalytic site for the substrate and the catalytic efficiency.
An allosteric inhibitor is referred to as an allosteric activator if it binds to an allosteric activator that increases the affinity of the enzyme to the substrate or the catalytic efficiency, whereas the affinity or catalytic efficiency of the enzyme substrate is reduced.
The effect of enzyme activity regulated by an allosteric agent is called allosteric regulation. The catalytic site of the allosteric enzyme and the allosteric site can coexist in different parts of one subunit, but more are on different subunits.
In the latter case, a subunit having a catalytic site is referred to as a catalytic subunit, and a subunit having an allosteric site is referred to as a regulatory subunit. Most of the allosteric enzymes are at the beginning of the metabolic pathway, and the allosteric enzymes of the allosteric enzymes are often some of the physiological small molecules and substrates for the action of the enzyme or intermediates or end products of the metabolic pathway.
Therefore, the catalytic activity of the allosteric enzyme is regulated by the concentration of the intracellular substrate, the concentration of the metabolic intermediate or the final product. The end product inhibits the allosteric enzyme in this pathway, called feedback inhibition.
It shows that once the end product in the cell increases, it acts as an allosteric inhibitor to inhibit the enzyme at the beginning of the metabolic pathway, and adjusts the speed of the metabolic pathway in time to adapt to the needs of the cell physiology. Allosteric enzymes play an important role in the regulation of cellular material metabolism. Therefore, an allosteric enzyme is also called a regulatory enzyme.
Some enzymes in the body need to be modified by other enzymes to modify the molecular structure of the enzyme. These enzymes are called modification enzymes. Among them, covalent modification is more common, such as the serine of the enzyme protein, the functional group -OH of the threonine residue can be phosphorylated, and then the modification of the covalent bond is generated, so it is called covalent modification (covalent Modification).
The change in enzyme activity due to this modification is called covalent modification regulation of the enzyme. The most common covalent modifications in the body are phosphorylation and dephosphorylation of enzymes, as well as enzymatic acetylation and deacetylation, uridine acidation and desurished, methylation and demethylation.
Because of the rapid covalent modification reaction and the cascade amplification effect, it is also an important way to regulate the metabolism of substances in the body.
For example, glycogen phosphorylase, which catalyzes the first step of glycogen decomposition, has both active and inactive forms, active phosphorylase a, and inactive phosphorylase b, both forms. Intermutation is the process of phosphorylation and dephosphorylation by enzyme molecules.
Multi-enzyme complex and multi-enzyme system
Some enzymes in the body are polymerized together to form a physical combination called a multienzyme complex. When the multi-enzyme complex is disintegrated, the catalytic activity of each enzyme disappears.
There are many enzymes involved in the formation of a multi-enzyme complex, such as a pyruvate dehydrogenase multi-enzyme complex that catalyzes the oxidative decarboxylation of pyruvate, composed of three enzymes, and a multi-enzyme complex that catalyzes the β-oxidation of fatty acids in mitochondria.
It consists of four enzymes. The product of the first enzyme-catalyzed reaction of the multi-enzyme complex becomes the substrate for the second enzyme, and thus proceeds continuously until the final product is formed.
Due to the physical combination, the multi-enzyme complex is beneficial to the rapid progress of the flow-through operation in the spatial conformation and is an effective measure for the organism to improve the catalytic efficiency of the enzyme.
The various pathways of material metabolism in the body often involve many enzymes, and the reaction process is completed in sequence. These enzymes are different from the multi-enzyme complex and are not related to each other in structure. It is called a multienzyme system. For example, 11 enzymes involved in glycolysis are present in the cytosol to form a multi-enzyme system.
In the 21st century, some enzyme molecules have been found to have various catalytic activities.
For example, E. coli DNA polymerase I am a molecular chain with a molecular mass of 109 kDa, which catalyzes the synthesis of DNA strands, 3′-5′ exonuclease and 5′-3. ‘Exonuclease activity, slightly hydrolyzed with proteolytic enzymes to obtain two peptides, one containing 5′-3’ exonuclease activity and the other containing two other enzyme activities, indicating E. coli DNA polymerase The molecule contains multiple active centers.
Mammalian fatty acid synthase consists of two polypeptide chains, each of which contains the catalytic activity of seven enzymes required for fatty acid synthesis. There are a number of catalytically active sites in the enzyme molecule of this enzyme called multifunctional enzyme (multifunctional enzyme) or tandem enzyme (tandem enzyme).
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Multi-functional enzymes are superior in molecular structure to multi-enzyme complexes because the associated chemical reactions are carried out on one enzyme molecule and are more efficient than multi-enzyme complexes, which is the result of biological evolution.