Chemical modification is different from allosteric regulation. It affects enzyme activity by causing changes in covalent bonds and chemical structures of enzyme molecules. The chemical modification of enzyme is completed under the catalysis of another enzyme, which is another important way of rapid regulation in the body. Chemical modification methods include phosphorylation and dephosphorylation, acetylation and deacetylation, methylation and demethylation, adenosylation and deadenylation, - SH and - S-S-tautomerism, etc. Among them, phosphorylation and dephosphorylation are the most important and common in metabolic regulation.
Phosphorylation and dephosphorylation of enzymes:
Phosphorylation It is a common form of decoration. Hydroxylated Amino acid residue Thr, Ser and Tyr can be used as phosphorylation modification sites. Phosphorylation is provided by ATP and completed under the catalysis of protein kinase. Dephosphorylation is catalyzed by phosphatase. Some enzymes have higher activity after phosphorylation, while others are inhibited after phosphorylation. It can be seen from the above that the chemical modification and regulation of enzyme have the following characteristics: ① It must be regulated by another Enzyme catalysis In addition, the mutual transformation between the active form of the enzyme and its inactive form is catalyzed by different enzymes in the positive and negative directions. ② The covalent bond on the enzyme molecule changes during the modification process, which changes the chemical structure of the enzyme. ③ The composition of enzyme molecule changes. The common forms of chemical modification are phosphorylation and dephosphorylation, but they can also be methylation, acetylation, etc. These chemical modifications can cause changes in the composition of enzyme molecules. ④ The chemical modification reaction of enzyme is catalyzed by enzyme, and the catalytic efficiency of enzyme is very high. One enzyme molecule can catalyze multiple agent molecules（ Enzyme protein ）The above composition changes occur, so there is amplification effect. Allosteric regulation and chemical modification regulation of enzymes both regulate the activity of existing enzymes and affect their activity by influencing the structure of existing enzymes. However, they are different in terms of whether other enzymes are required to participate, whether there are changes in covalent bonds of enzyme molecules, and whether there are changes in composition.
Comparison of allosteric regulation and chemical modification of enzyme:
In addition, in terms of regulation, allosteric regulation mostly affects the key enzyme (the enzyme at the metabolic turning point) to cause directional changes in metabolism; The chemical modification regulation takes the amplification effect to regulate the metabolic intensity as the main role. But we should also see that their roles are complementary and cannot be completely divided. Sometimes these two regulation modes can coexist. Some enzymes have dual regulation of allosteric and chemical modification.
(1) The vast majority of enzymes belonging to this type of regulation have two forms: inactive (or low activity) and active (or high activity). They can be covalently modified under the catalysis of two different enzymes, and can transform each other. Enzymes that catalyze tautomeric reactions are controlled by regulatory factors such as hormones in vivo.
(2) Different from allosteric regulation, chemical modification is a covalent bond change caused by enzyme catalysis, and because it is an enzymatic reaction, it has amplification effect. Long catalytic efficiency is higher than allosteric regulation.
(3) Phosphorylation and dephosphorylation are the most common enzymatic chemical reactions.
