What is an enzyme, its composition, functions and classification of each part?

enzyme refers to a high molecular substance with biocatalysis function. In the catalytic reaction system of enzyme, the reactant molecule is called substrate, and the substrate is converted into another molecule through the catalysis of enzyme. Almost all cell activity processes need the participation of enzymes to improve efficiency. Similar to other non-biological catalysts, enzymes can accelerate the reaction rate by reducing the activation energy of chemical reactions (expressed by Ea or δ G), and most enzymes can increase the reaction rate catalyzed by them by millions of times. In fact, enzyme is another way to provide lower activation energy demand, so that more reaction particles can have kinetic energy not less than activation energy, thus accelerating the reaction rate. As a catalyst, the enzyme itself is not consumed in the reaction process, nor does it affect the chemical balance of the reaction. Enzymes have both positive and negative catalytic effects, which not only accelerate the reaction rate, but also reduce the reaction rate. Different from other non-biological catalysts, enzymes are highly specific and only catalyze specific reactions or produce specific configurations.

although most enzymes are protein, a few molecules with biocatalytic function are not protein, and some RNA molecules called ribozymes have the same catalytic function as some DNA molecules. In addition, the so-called artificial enzyme synthesized artificially also has catalytic activity similar to that of enzyme. Some people think that enzymes should be defined as biomacromolecules with catalytic function, that is, biocatalysts. [1]

The catalytic activity of the enzyme is influenced by other molecules: inhibitors are molecules that can reduce the activity of the enzyme; Activators are molecules that can increase the activity of enzymes. Many drugs and poisons are inhibitors of enzymes. Enzyme activity can also be affected by many factors, such as temperature, chemical environment (such as pH value), substrate concentration and electromagnetic wave (such as microwave).

there are 5 kinds of enzymes in human and mammals. They are either dissolved in the cytoplasm, or combined with various membrane structures, or located in specific positions of other structures in cells (a product of cells), and are activated only when needed. These enzymes are collectively called intracellular enzymes; In addition, there are some enzymes that are synthesized in cells and then secreted out of cells-extracellular enzymes. The ability of enzymes to catalyze chemical reactions is called enzyme activity (or enzyme activity). Enzyme activity can be regulated and controlled by many factors, so that organisms can adapt to the changes of external conditions and maintain life activities. Without the participation of enzymes, metabolism can hardly be completed and life activities can not be maintained at all.

all enzymes contain four elements: c, h, o and n.

Enzymes are a kind of biocatalysts. There are thousands of enzymes in organisms, which dominate many catalytic processes such as metabolism, nutrition and energy conversion. Most of the reactions closely related to life processes are enzyme-catalyzed reactions. But enzymes do not necessarily play a catalytic role only in cells.

the essence of enzyme catalysis is to reduce the activation energy of chemical reaction.

Compared with inorganic catalysts, enzymes have the following characteristics:

1. Similarities: 1) Changing the chemical reaction rate hardly consumes itself; 2) only catalyze existing chemical reactions; 3) accelerate the chemical reaction rate and shorten the time to reach equilibrium, but do not change the equilibrium point; 4) Reduce the activation energy and accelerate the chemical reaction rate. 5) Poisoning will occur.

2. Differences: the characteristics of the enzyme, including high efficiency, specificity, gentleness (requiring a certain pH and temperature), etc.

source

The so-called Enzyme, in Greek, means that it exists in yeast. That is, all kinds of substances that carry out life activities in yeast are found and then named like this. At this time, "yeast" is always a living organism = microorganism, "enzyme" is a living substance = an incredible substance that produces life activities (it may be better to call it a living substance according to the image).

But enzyme is not equal to yeast: it can only be said that yeast contains the most kinds of enzymes and enzymes per unit volume of all living things in nature! Especially beer yeast!

Yeast is a single-celled microorganism, which contains many enzymes. Yeast has cell tissue, while enzyme is protein. Usually, there are thousands of protein in a yeast, so yeast contains enzymes, but enzymes are not equal to yeast.

classification:

according to the different properties of the reactions catalyzed by enzymes, enzymes can be divided into six categories:

oxidoreductase

an enzyme that promotes the oxidation-reduction reaction of substrates, which is a kind of enzyme that catalyzes the oxidation-reduction reaction and can be divided into oxidase and reductase. [6]

Transferases

Enzymes that catalyze the transfer or exchange of certain groups (such as acetyl, methyl, amino, phosphate, etc.) between substrates. For example, methyltransferase, aminotransferase, acetyltransferase, thiotransferase, kinase and polymerase.

hydrolases

Enzymes that catalyze the hydrolysis of substrates. For example, amylase, protease, lipase, phosphatase, glycosidase, etc.

lyases are enzymes that catalyze the reaction of removing a group from a substrate (non-hydrolysis) and leaving a double bond or its reverse reaction. For example, dehydratase, decarboxylase, carbonic anhydrase, aldolase, citrate synthase, etc. Many lyases catalyze the reverse reaction, forming new chemical bonds between two substrates and eliminating the double bond of one substrate. Synthases fall into this category.

Isomerases

(isomerases) Enzymes that catalyze the conversion between various isomers, geometric isomers or optical isomers. For example, isomerase, epizyme, racemase, etc.

synthetase

(ligase) catalyzes the synthesis of two molecules of substrates into one molecule of compounds, and at the same time, the phosphate bond coupled with ATP is broken to release energy. For example, glutamine synthetase, DNA ligase, amino acid: tRNA ligase and biotin-dependent carboxylase.

According to the unified classification principle of enzymes published by the International Biochemical Association, on the basis of the above six categories, each category of enzymes is divided into several subcategories according to the characteristics of the groups or bonds acted on in the substrate; In order to show the properties of substrates or reactants more accurately, each subclass is divided into several groups (subclasses); Each group directly contains several enzymes.

function:

catalysis

acid-base catalysis: the catalysis of proton transfer to accelerate the reaction.

* * valence catalysis: a substrate or a part of a substrate forms a * * * valence bond with the catalyst and then is transferred to the second substrate. Many enzyme-catalyzed group transfer reactions are carried out by valence.

catalytic mechanism

The catalytic mechanism of an enzyme is basically the same as that of a general chemical catalyst, that is, it combines with a reactant (the substrate of the enzyme) to form a complex, and the speed of the chemical reaction is increased by reducing the energy of the reaction. At a constant temperature, although the energy contained in each reactant molecule in the chemical reaction system is quite different, its average value is low, which is the initial state of the reaction.

the reaction of s (substrate) →P (product) can be carried out because a considerable part of s molecules have been activated into activated (transition state) molecules, and 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 make all molecules of one mole of a substance become activated molecules.

the function of enzyme (e) is to temporarily combine with s to form a new compound ES, and the activation state (transition state) of ES is much lower than that of the reactant activation molecules in the chemical reaction without catalyst. ES reacts again to produce p and release e at the same time. E can combine with other S molecules and repeat this cycle. Reduce the activation energy required for the whole reaction, so that more molecules can react in unit time, and the reaction speed can be accelerated. If there is no catalyst, the reaction (2H2O2→2H2O+O2) in which hydrogen peroxide is decomposed into water and oxygen requires an activation energy of 18 kcal per mole (1 kcal =4.187 Joule). When catalase is used to catalyze this reaction, the activation energy is only 2 kcal per mole, and the reaction speed is increased by about 1.11 times.

reaction

characteristics

Enzymes are efficient biocatalysts, which are 17-113 times more efficient than ordinary catalysts. Enzymes can speed up the chemical reaction, but they can't change the equilibrium point of the chemical reaction, that is to say, the enzyme can promote the forward reaction as well as the reverse reaction in the same proportion, so the function of the enzyme is to shorten the time needed to reach the equilibrium, but the equilibrium constant remains unchanged. It takes several hours to reach the equilibrium point without enzyme, and it may take only a few seconds to reach the equilibrium point with enzyme.

both enzymes and general catalysts accelerate the chemical reaction by reducing the activation energy. The catalytic specificity of

enzyme lies in its selectivity to substrate and specificity of catalytic reaction. In addition to individual spontaneous chemical reactions in the body, most of them are catalyzed by specific enzymes. An enzyme can find its own substrate from thousands of reactants, which is the specificity of the enzyme. According to the difference in the degree of specificity of enzyme catalysis, it can be divided into three categories: absolute specificity, relative specificity and stereoisomeric specificity. An enzyme that catalyzes only one substrate is called absolute specificity. For example, urease can only hydrolyze urea to decompose it 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. For example, esterase can not only catalyze the hydrolysis of triglycerides, but also hydrolyze other ester bonds. Enzymes with stereoisomeric specificity have strict requirements on the stereoconfiguration of substrate molecules. For example, L- lactate dehydrogenase only catalyzes the dehydrogenation of L-lactic acid, but has no effect on D- lactic acid.

the catalytic activity of some enzymes can be influenced by many factors, such as allosteric enzymes being regulated by allosteric agents, some enzymes being regulated by valence modification, hormones and neurohumors regulating the activity of enzymes through second messengers, and inducers or inhibitors regulating the content of enzymes in cells (changing the speed of enzyme synthesis and decomposition).

mechanism of action

enzyme (e) and substrate (s) form an enzyme-substrate complex (ES)

it is the first step of enzyme catalysis to directionally combine the active center of enzyme with substrate to form an ES complex. The energy of directional binding comes from various non-* * valence bonds formed when the functional groups in the enzyme active center interact with the substrate, such as ionic bonds, hydrogen bonds and hydrophobic bonds, including van der Waals force. The energy generated when they combine is called binding energy. It is not difficult to understand that each enzyme is selective in binding to its own substrate.

if the enzyme only complements the substrate to form an ES complex, which can not further promote the substrate to enter the transition state, then the catalysis of the enzyme cannot occur. This is because after the enzyme and substrate form the ES complex, it is necessary to form more non-* * valence bonds between the enzyme and substrate molecules to form the complex with complementary transition states between the enzyme and substrate (Figure 4-8), so as to complete the catalytic action of the enzyme. In fact, in the process of generating more non-* * valence bonds, the substrate molecules change from the original ground state to the transition state. That is, the substrate molecules become activated molecules, which provides conditions for the combination and arrangement of groups needed for the chemical reaction of the substrate molecules, the generation of instantaneous unstable charges and other transformations. Therefore, the transition state is not a stable chemical substance, which is different from the intermediate product in the reaction process. As far as the transition state of a molecule is concerned, the probability of its transformation into product (P) or substrate (S) is equal.

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

1. Proximity effect and directional arrangement

2. multielement catalysis)

3． p > 3. Surface effect

It should be pointed out that the catalytic reaction of an enzyme is often a combination of various catalytic mechanisms, which is an important reason why enzymes promote the high efficiency of the reaction.

Application of enzymes:

Catalysts

Enzymes in organisms are biologically active protein, which exists in cells and tissues of organisms. As a catalyst for chemical reactions in organisms, they constantly renew themselves, so that the complex metabolic activities in organisms can be carried out continuously and orderly.

High efficiency and specificity

The catalytic efficiency of enzymes is particularly high (that is, high efficiency). The efficiency is 1.7 ~ 1.18 times higher than that of ordinary chemical catalysts, which is one of the reasons why many chemical reactions in organisms are easy to carry out.

The catalysis of enzymes has high chemical selectivity and specificity. An enzyme can only catalyze a certain reaction or a certain kind of reaction, and the enzyme and the catalyzed reactants are often similar in structure.

Generally, at about 37℃, in a neutral environment, the enzyme Although it is the same as the general catalyst, its activity increases with the increase of temperature, but because the enzyme is protein, it will lose its activity (denaturation) if the temperature is too high, so the catalytic temperature of the enzyme should not be higher than 6℃, otherwise, the catalytic efficiency of the enzyme will be reduced or even lose its catalytic effect. The existence of strong acid, strong alkali, heavy metal ions and ultraviolet rays will also affect the catalytic effect of the enzyme. < P > Function in human body < The structure is complex, and there are many kinds. Up to now, more than 3, kinds (diversity) have been found. For example, when rice is chewed in the mouth, the longer the chewing time, the more obvious the sweetness is, because the starch in rice is hydrolyzed into maltose under the action of salivary amylase secreted by the mouth. Therefore, chewing more during meals can make food and saliva fully mixed, which is beneficial to digestion. In addition, there are pepsin in the body. Trypsin and other hydrolases. protein ingested by human body from food must be hydrolyzed into amino acids under the action of pepsin and other enzymes, and then more than 2 kinds of amino acids needed by human body are selected and recombined into various protein needed by human body in a certain order, in which many complex chemical reactions have taken place. It can be said that without enzymes, there would be no biological metabolism. There would be no various and colorful biological worlds in nature. [7]

Physiological and medical effects of enzymes

Relationship between enzymes and certain diseases

Diseases caused by enzyme deficiency are mostly congenital or hereditary, such as albinism due to tyrosine hydroxylase deficiency. Patients with bean disease or sensitive to primary aminoquinoline are due to the deficiency of glucose 6-phosphate dehydrogenase. Many toxic diseases are almost caused by the inhibition of some enzymes. For example, when common organophosphorus pesticides (such as trichlorfon, dichlorvos, 159 and dimethoate) are poisoned, it is because they combine with a-OH on serine, an essential group in the active center of cholinesterase that the enzyme loses its activity. Cholinesterase can catalyze the hydrolysis of acetylcholine into choline and acetic acid. When cholinesterase is inhibited and inactivated, the hydrolysis of acetylcholine is inhibited, resulting in the accumulation of acetylcholine and a series of poisoning symptoms, such as muscle tremor, pupil contraction, hyperhidrosis, and slow heartbeat. Some metal ions cause human poisoning, because metal ions (such as Hg2+) can combine with the necessary groups of some enzyme activity centers (such as-SH of cysteine) and make the enzyme inactive.