What Is the Connection Between Enzymes and Temperature?

Enzyme catalysis, also known as enzyme catalysis or enzyme catalysis, refers to a chemical reaction catalyzed by an enzyme as a catalyst.

Enzymes are specific and efficient biocatalysts. Most enzymes are proteins produced by living cells. Enzymatic conditions are mild and can be carried out at normal temperature and pressure. Enzymatic reactions are called enzymatic reactions, which are 103-107 times faster than the corresponding non-catalytic reactions. The kinetics of enzymatic reaction is referred to as enzyme kinetics, which mainly studies the relationship between the speed of enzymatic reaction and the concentration of substrate (ie reactant) and other factors. When the substrate concentration is low, the enzymatic reaction is a first-order reaction; when the substrate concentration is in the middle range, it is a mixed-stage reaction; when the substrate concentration increases, it transitions to a zero-order reaction ^[1]

Temperature, pH, enzyme concentration, concentration of catalyzed substance, inhibitor, activator, reaction product

Effect of substrate concentration on the rate of enzyme reaction

The influence of substrate concentration on the reaction speed of enzyme is more complicated. When the substrate concentration is low at a certain enzyme concentration

Under certain temperature and pH conditions, when the substrate concentration is sufficient to saturate the enzyme

In the case, the concentration of the enzyme is proportional to the speed of the enzymatic reaction. Right:

Effect of pH on the rate of enzyme reaction

Effect of pH on the rate of enzymatic reaction The pH of the enzyme reaction medium can affect the enzyme molecule, especially the degree of dissociation of the necessary groups on the active center and the ionization state required by the proton donor or proton acceptor in the catalytic group. Can affect the degree of dissociation of substrates and coenzymes, thereby affecting the binding of enzymes and substrates. Only under specific pH conditions, the dissociation of enzymes, substrates and coenzymes is most suitable for them to combine with each other and catalyze to maximize the rate of enzymatic reaction. This pH value is called the optimal enzyme pH.

The activity of most trypsin enzymes is affected by its environmental pH. At a certain pH, the enzymatic reaction has the maximum speed. Above or below this value, the reaction will decline. This pH is usually called the optimal pH of the enzyme. The optimum pH is different for different enzymes.

Right: For example: the optimum pH of pepsin is 1.5 ~ 2.2, the optimum pH of trypsin is 8.0 ~ 9.0, and the optimum pH of salivary amylase is 6.8. Animal enzymes are mostly between pH 6.5 and 8.0, and plants and microorganisms are mostly between pH 4.5 and 6.5, but there are exceptions. For example, the optimum pH for fungi is 5.0 ~ 6.0, the optimum for most bacteria is 6.5 ~ 7.5, and the optimum for actinomycetes is 7.5 ~ 8.5.

The optimal pH of most enzymes in the body is close to neutral, but there are exceptions. For example, the optimal pH of pepsin is about 1.8, and the optimal pH of liver arginase is about 9.8. When the pH value of the solution is higher and lower than the optimal pH, the enzyme activity will be reduced, and when it is far away from the optimal pH value, it will even cause the enzyme to denature and inactivate (Figure). Therefore, when measuring enzyme activity, a suitable buffer should be selected to keep the enzyme activity relatively constant. According to clinical characteristics of pepsin's optimal pH and partial acidity, a certain amount of dilute hydrochloric acid is added to prepare a digestive pepsin mixture, so that it can exert better curative effect.

Main reasons why pH affects enzyme activity

Peracid and alkali affect the structure of the enzyme molecule, and even inactivate the enzyme.

It should be noted that the optimal pH of the enzyme in a test tube is not necessarily exactly the same as its physiological pH in normal cells. This is because there may be hundreds of enzymes in a cell, and different enzymes have different sensitivity to the physiological pH in the cell; that is to say, this pH is the optimal pH for some enzymes and not for other enzymes. Different enzymes show different activities. This difference may be significant for controlling complex metabolic pathways within cells.

Effect of temperature on the speed of enzymatic reactions

The speed of chemical reactions increases with increasing temperature, but enzymes are proteins that can be denatured with increasing temperature. When the temperature is low, the former influence is greater, and the reaction speed increases with the increase of temperature. However, when the temperature exceeds a certain range, the thermal denaturation of the enzyme is dominant, and the reaction rate slows down as the temperature rises. The temperature range with the maximum enzymatic reaction rate is often referred to as the optimal temperature of the enzyme

The optimum temperature of the enzyme in the human body is close to the body temperature, generally between 37 ° C and 40 ° C. If the enzyme is heated to 60 ° C, it will begin to denature. Above 80 ° C, the enzyme's denaturation is irreversible.

The effect of temperature on the speed of enzymatic reactions has guiding significance in clinical practice. Under low temperature conditions, the enzyme activity decreases, but the enzyme is generally not destroyed at low temperatures. After the temperature rises, the enzyme activity is restored. Therefore, in the operation of management technology, enzyme preparations and enzyme test specimens (such as serum) should be stored in the refrigerator at low temperature, removed from the refrigerator when needed, and used or tested after the temperature rises at room temperature. After the temperature exceeds 80 ° C, most enzymes are denatured and inactivated, and this principle is clinically applied for high-temperature sterilization.

The optimum temperature of the enzyme is related to the time required for the reaction. The enzyme can tolerate higher temperatures in a short period of time. On the contrary, the longer the reaction time, the lower the optimum temperature. Accordingly, in the biochemical test, a method of appropriately increasing the temperature and shortening the time can be adopted to perform rapid detection of the enzyme.

Different temperatures have different effects on activity, but they all have an optimum temperature. On both sides of the optimum temperature,

The reaction speed is relatively low. Right:

The effect of temperature on the enzymatic reaction includes two aspects: On the one hand, when the temperature increases, the reaction speed also accelerates, which is the same as the general chemical reaction. On the other hand, the enzyme is gradually denatured with increasing temperature, that is, the reaction speed of the enzyme is reduced by reducing the active enzyme. When the temperature is lower than the optimal temperature, the former effect is dominant, and when the temperature is higher than the optimal temperature, the latter effect is dominant. Therefore, the enzyme activity is lost and the reaction speed decreases.

In the process of preparing the culture medium, the culture medium can be sterilized by using high temperature, which mainly destroys the enzyme activity in the microorganism. High temperature sterilization is widely used in medicine and life practice.

Under low temperature conditions, the enzyme activity decreases, but the structure of the enzyme molecule generally changes. Therefore, one can choose to store the enzyme at low temperatures. In daily life, people often choose to keep food at low temperature for a long time.

The role of enzyme inhibitors

The effect of reducing or losing the enzyme activity by changing the chemical properties of the necessary groups of the enzyme is called inhibitory effect, and the substance with the inhibitory effect is called inhibitor. The inhibitor is usually a small molecule compound, but there are biological macromolecules Type of inhibitor.

Classification of inhibitors of enzymes

Enzyme inhibitors are divided into two categories: irreversible inhibitors and reversible inhibitors. The irreversible inhibitor is covalently bonded to the essential group of the enzyme, causing permanent inactivation of the enzyme, and its inhibitory effect cannot be removed by isothermal and physical means such as dialysis, ultrafiltration. Reversible inhibitors and enzyme proteins are bound by non-covalent bonds, causing temporary loss of enzyme activity, and their inhibitory effects can be relieved by dialysis, ultrafiltration and other means. Reversible inhibitors are divided into competitive inhibitors, non-competitive inhibitors and anti-competitive inhibitors.

The role of enzymatic reaction activators

Enzyme activity can be enhanced by certain substances, which are called activators. Adding an activator to the manifestation of an enzymatic reaction can lead to an increase in the reaction rate. Generally, enzymes have certain selectivity to activators, and have certain concentration requirements. An activator of one enzyme may be an inhibitor to another enzyme. When the concentration of an activator exceeds a certain range, it becomes an inhibitor ^{[1 ]} .