The International Union of Biochemistry and Molecular Biology systematically classifies enzymes into seven major categories based on the type of catalytic reactions they mediate.
1. Oxidoreductases
Core function: Catalyze oxidation-reduction reactions in organisms, i.e., the transfer of electrons between different molecules. These enzymes typically require coenzymes for activity, with common examples including oxidases and peroxidases. For instance, glucose oxidase catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide, and is widely used in food preservation to inhibit microbial growth.
2. Transferases
Core function: Catalyze the transfer of functional groups from one molecule to another. A classic example is transaminase, which transfers amino groups between amino acids and keto acids, serving as a key enzyme in protein metabolism. For example, transglutaminase catalyzes cross-linking between protein molecules, and is commonly used in the food industry to improve the elasticity of meat products and the stability of dairy products.
3. Hydrolases
Core function: Catalyze hydrolysis reactions of substrates, i.e., breaking down macromolecules into smaller ones by adding water molecules. This class includes amylases, proteases, lipases, etc. α-Amylase in saliva hydrolyzes starch in rice and noodles into maltose, allowing us to taste sweetness. The catalytic reactions of hydrolases are usually irreversible, making them the core force in the catabolism of substances in living organisms.
4. Lyases
Core function: Catalyze the non-hydrolytic cleavage or formation of chemical bonds, leading to molecular cleavage or cyclization, with double bonds often generated during the reaction. For example, carbonic anhydrase catalyzes the reaction between carbon dioxide and water to form carbonic acid, which is used in food processing to regulate the stability of bubbles in carbonated beverages.
5. Isomerases
Core function: Catalyze isomerization reactions of molecules, i.e., changes in spatial structure or chemical bond arrangement without altering the atomic composition. Glucose isomerase is the most widely used isomerase, primarily catalyzing the reversible isomerization of glucose to fructose. In the production of high-fructose corn syrup, it converts glucose into fructose to enhance sweetness.
6. Ligases
Core function: Catalyze the ligation of two molecules into a macromolecule, a process usually requiring energy sources such as ATP. For example, DNA ligase is a core tool in genetic engineering for constructing recombinant DNA molecules. Reactions catalyzed by ligases are key steps in macromolecule synthesis in organisms, playing a crucial role in genetic information transmission and substance synthesis.
7. Translocases
The seventh category, added in 2018, catalyzes the transport of ions or molecules across biological membranes or their transfer between different molecules. These reactions are typically associated with the material transport function of biological membranes. The inclusion of translocases has completed the enzyme classification system, covering the important physiological process of substance transport in living organisms.