Classification of Enzymes in Details: 

• To study enzymes with different properties and functions, a systematic and effective classification method is necessary.
• Although the molecular composition and cellular localization of enzymes can be used as a basis for classification.
• For functional research, it is more important to classify enzymes according to the type of reaction they catalyze.
• In 1961, the International Union of Biochemistry and Molecular Biology (IUBMB) grouped all enzymes into six categories according to the type of reaction they catalyze. 
• In August 2018, the classification of translocases was added, so there are now seven major enzymes, namely: oxidase-reductase (EC 1), transferase (EC 2), hydrolase (EC 3), lyase (EC 4), isomerase (EC 5), ligase (EC 6) and translocase (EC 7). Wherein EC stands for Enzyme Commission.
• In these seven major enzyme classes (class), each is divided into several subclasses (subclass), and subclasses are divided into sub-subclasses (sub-subclass). 
• The classification criteria of subclasses are different according to the characteristics of each type of reaction.

1. Oxidoreductases (EC 1): 

• These enzymes catalyze oxidation-reduction reactions.
• According to the principle of systematic classification enzymes oxidoreductases are divided into 24 subclasses according to the type of electron donor (substrate) and the sub-subclasses are divided according to the electron acceptor.
• The coenzymes of this class are NAD, NADP, FAD, FMN, ubiquinone, glutathione, and lipoic acid.
• Oxidoreductase enzymes help in energy production, detoxification, and other functions that are extremely important to living organisms.

Subclasses of Oxido-reductases Enzymes:

If we consider all subclasses, then groups of enzymes acting on are :

• 1.1. CH-OH donor group;
• 1.2. aldehyde or ketone group of donors;
• 1.3. CH-CH group of donors;
• 1.4. CH-NH 2 donor group;
• 1.5. CH-NH donor group;
• 1.6. NADH or NADPH as donors;
• 1.8. containing sulfur groups of donors;
• 1.9. heme-containing donors;
• 1.10. diphenols as donors;
• 1.11. hydrogen peroxide as an acceptor;
• 1.11. hydrogen as a donor;
• 1.13. one donor with the inclusion of molecular oxygen;
• 1.14. two donors with the inclusion of molecular oxygen;
• 1.15. superoxide radicals as an acceptor;
• 1.17. CH 2 group of donors;
• 1.18. ferredoxin as a donor;
• 1.19. flavodoxin as a donor;
• 1.20. phosphorus or arsenic as a donor;
• 1.21. on substances X-H and Y-H with the formation of an XY-bond;
• 1.22. halogen as a donor;
• 1.97. other oxidoreductases

Examples of Oxido-reductases Enzymes: 

The most common names for oxidoreductase enzymes are:

• Oxidases: are oxidoreductases that catalyze the oxidation of substrates with molecular oxygen as an electron acceptor without incorporating oxygen into the substrate molecule.

• Dehydrogenases: are oxidoreductases that catalyze the dehydrogenation of a substrate using any molecules other than oxygen as a hydrogen acceptor. For example, alcohol dehydrogenase has an EC number of 1.1.1.1. – it is an oxidoreductase that acts on the OH group of the donor with NAD as an acceptor with the first serial number in its subclass; lactate dehydrogenase – EC 1.1.1.27, acts on the OH group of the donor with NAD as an acceptor with serial number 27 in its subclass.

• Reductases: If the transfer of hydrogen from a donor molecule is difficult to prove, then such oxidoreductases are called reductases.

• Peroxidases are oxidoreductases that catalyze reactions with hydrogen peroxide as an electron acceptor.

• Monooxygenases: are oxidoreductases that catalyze the introduction of one oxygen atom into a substrate molecule with molecular oxygen as an oxygen donor.

• Dioxygenases: are oxidoreductases that catalyze the introduction of 2 oxygen atoms into a substrate molecule with molecular oxygen as an oxygen donor.

2. Transferase (EC 2): 

• Transferases catalyze the reactions of the transfer of various functional groups from one substrate (donor) to another (acceptor).
• These enzymes take place in the interconversion of various substances, neutralizing natural and foreign compounds. 
• The coenzymes of transferases are pyridoxal phosphate, coenzyme A, tetrahydrofolic acid, and methylcobalamin. 
• The class is subdivided into 9 subclasses depending on the structure of the transferred groups.

Subclasses of Transferases Enzymes:

If we consider all  subclasses, then groups of enzymes are distinguished in them depending on the composition of the transferred group

• 2.1. transferring one-carbon fragments;
• 2.2. carrying aldehyde and keto groups;
• 2.3. carrying acyl groups;
• 2.4. carrying glycosyl groups;
• 2.5. carrying non-methyl alkyl and aryl groups;
• 2.6. transferring nitrogen-containing groups;
• 2.7. carrying phosphorus-containing groups.
• 2.8. transferring sulfonic groups;
• 2.9. carrying selenium-containing groups.

Examples of Transferases Enzymes: 

• Carbonyltransferases (EC 2.1): Transfer of one-carbon units, such as methyltransferases involved in the methylation of nucleic acids and proteins. Carboxyltransferases belong to this subclass, such as methylmalonyl-CoA carboxyltransferases (EC 2.1.3.1).

• Glycosyltransferase (EC 2.4): closely related to carbohydrate metabolisms, such as glycogen synthase (2.4.1.11), and glycogen phosphorylase (2.4.1.1).

• Phosphotransferases (EC 2.7): Often called kinases, mostly use ATP as a donor. For example, hexokinase, protein tyrosine kinase, etc. It is important to note that a few proteases are also called kinases (eg enterokinase), but they are hydrolases.