The ability of an enzyme to catalyze chemical reactions is called enzyme activity (or enzyme activity, active unit). The 1961 International Enzymology Conference stipulated that one unit of enzyme activity refers to the amount of enzyme that can convert 1 μmol of substrate in 1 minute under specific conditions (25°C, other suitable conditions), or the amount of enzyme that can convert 1 μmol of the relevant radical in the substrate. The amount of enzyme in the group.

Influencing factors

Enzyme activity can be regulated and controlled by a variety of factors, allowing organisms to adapt to changes in external conditions and maintain life activities. Without the participation of enzymes, metabolism is almost impossible to maintain. The enzyme activity index uses enzyme activity units and it can be known from the Rice equation: the enzymatic reaction speed is affected by the enzyme concentration and substrate concentration, as well as by temperature, pH, activators and inhibitors.

(1) Enzyme concentration

It can be seen from the Rice equation and the diagram of the relationship between enzyme concentration and enzymatic reaction rate: the enzymatic reaction rate is directly proportional to the concentration of enzyme molecules. When the concentration of substrate molecules is sufficient, the more enzyme molecules there are, the faster the substrate is converted. But in fact, when the enzyme concentration is very high, this relationship is not maintained and the curve gradually becomes flat. According to analysis, this may be caused by the high concentration of substrate entrained with many inhibitors.

(2)Substrate concentration

In biochemical reactions, if the concentration of the enzyme is a constant value and the initial concentration of the substrate is low, the enzymatic reaction rate is proportional to the substrate concentration, that is, it increases as the substrate concentration increases. When all enzymes combine with the substrate to form intermediate products, even if the substrate concentration is increased, the concentration of the intermediate products will not increase, and the enzymatic reaction rate will not increase.

It can also be concluded that under the same conditions of substrate concentration, the enzymatic reaction rate is proportional to the initial concentration of enzyme. The greater the initial concentration of enzyme, the greater the enzymatic reaction rate.

In actual measurements, even if the enzyme concentration is high enough, as the substrate concentration increases, the enzymatic reaction rate does not increase or is even inhibited. The reason is that high-concentration substrates reduce the effective concentration of water and reduce molecular diffusivity, thereby reducing the enzymatic reaction speed. Excess substrate accumulates on the enzyme molecules, generating inactive intermediates that cannot release the enzyme molecules, thereby also reducing the reaction speed.

(3)Temperature

Various enzymes have strong enzymatic activity and high enzymatic reaction speed within a suitable temperature range. Within a suitable temperature range, for every 10°C increase in temperature, the enzymatic reaction rate can increase by 1 to 2 times. The suitable temperatures for enzymes in different organisms are different. For example, the suitable temperature of various enzymes in animal tissues is 37~40℃; the suitable temperature of various enzymes in microorganisms is 25~60℃, but there are exceptions, such as the suitable temperature of niger glucoamylase is 62~64℃; giant The optimum temperature for glucose isomerase in Bacillus, Lactobacillus brevis, and Aerobacillus aerogenes is 80°C; the optimum temperature for liquefied amylase of Bacillus subtilis is 85 to 94°C. It can be seen that the thermal stability of some Bacillus enzymes is relatively high. Temperatures that are too high or too low will reduce the catalytic efficiency of the enzyme, that is, reduce the speed of the enzymatic reaction.

For enzymes with a suitable temperature below 60°C, when the temperature reaches 60 to 80°C, most of the enzymes are destroyed and undergo irreversible denaturation; when the temperature approaches 100°C, the catalytic effect of the enzyme is completely lost. This is why people don’t want to eat when they have a fever.

(4)pH

Enzymes exhibit activity within a suitable pH range. If the pH is greater than or less than the suitable pH, the enzyme activity will be reduced. Mainly manifested in two aspects: ① changing the charged state of substrate molecules and enzyme molecules, thereby affecting the combination of enzyme and substrate; ② too high or too low pH will affect the stability of the enzyme, thereby causing the enzyme to suffer irreversible damage. The closer the pH value of most enzymes in the human body is to 7, the better the catalytic effect. However, pepsin in the human body is suitable for an environment with a pH value of 1 to 2, and the suitable pH for trypsin is around 8.

(5)Activator

Substances that can activate enzymes are called enzyme activators.

Activator Type:

①Inorganic cations, such as sodium ions, potassium ions, copper ions, calcium ions, etc.;

②Inorganic anions, such as chloride ions, bromide ions, iodide ions, sulfate ions, phosphate ions, etc.;

③Organic compounds, such as vitamin C, cysteine, reduced glutathione, etc. Many enzymes only show catalytic activity or enhance their catalytic activity in the presence of an appropriate activator, which is called activation of the enzyme. Some enzymes are in an inactive state after being synthesized, and these enzymes are called zymogens. It must be activated by an appropriate activator to become active.

(6)Inhibitors

Substances that can weaken, inhibit or even destroy enzyme activity are called enzyme inhibitors. It can reduce the speed of enzymatic reactions. Enzyme inhibitors include heavy metal ions, carbon monoxide, hydrogen sulfide, hydrocyanic acid, fluoride, iodoacetic acid, alkaloids, dyes, p-chloromercuric benzoic acid, diisopropylfluorophosphoric acid, ethylenediaminetetraacetic acid, surface Active agents, etc.

Inhibition of enzymatic reactions can be divided into competitive inhibition and non-competitive inhibition. Substances with a similar structure to the substrate compete to bind to the active center of the enzyme, thereby reducing the speed of the enzymatic reaction. This effect is called competitive inhibition. Competitive inhibition is reversible inhibition, which can be relieved by increasing the substrate concentration and restoring enzyme activity. Substances that are structurally similar to the substrate are called competitive inhibitors. After the inhibitor binds to a site other than the active center of the enzyme, the substrate can still bind to the active center of the enzyme, but the enzyme does not show activity. This effect is called non-competitive inhibition. Noncompetitive inhibition is irreversible, and increasing substrate concentration cannot relieve the inhibition of enzyme activity. Inhibitors that bind to sites other than the active center of an enzyme are called noncompetitive inhibitors.

Some substances can act as both inhibitors of one enzyme and activators of another.