Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Enzymes
List of enzymes

Based on this system, which serves as the foundation for both Classification and numbering (indexing) of Enzymes, the International Commission also prepared the Enzyme Nomenclature (EC), which initially included a list of about 900 enzymes as of 1961. By the time of the 1978 Enzyme Nomenclature update, the list already contained 2,142 individual enzymes, and by December 1995, more than 3,500 had been identified. For each enzyme, the list provides a code number (EC number), a systematic (rational) name, a recommended (working) name, the chemical reaction catalyzed by the enzyme, and notes on reaction Specificity. Each enzyme is assigned a four-part code number.

Thus, the code of each enzyme consists of four digits separated by periods and is constructed according to a specific principle. The first digit indicates the main Class, representing one of the six primary enzyme classes. The second digit denotes the subclass, which characterizes the MAIN TYPES OF substrates involved in that specific chemical transformation. For example, in transferases, the second digit indicates The Nature of the group being transferred; in Hydrolases, it specifies the type of bond being hydrolyzed, and so on. These subclasses are further divided into more specific sub-subclasses, distinguished by the Nature of the donor or acceptor chemical compounds involved in that group of reactions. The sub-subclass number (digit) occupies the 3rd position in the enzyme code. For hydrolases, for instance, this digit clarifies the type of bond hydrolyzed, whereas for lyases, it specifies the type of group eliminated, and so on. The first three digits of the code precisely define the type of enzyme. Finally, all enzymes belonging to a given sub-subclass are assigned a serial number in alphabetical order, which occupies the 4th position in the code.

Table 4.6. Fragment from the Enzyme List

Each enzyme, characterized by a consistent set of 4 digits, corresponds to a unique code under which it is entered into the enzyme list. As an example, Table 4.6 presents two enzymes from this list.

It should be emphasized that the International Enzyme Classification cannot be considered entirely flawless, as in certain respects it does not align with the classification of Chemical Reactions generally accepted in organic chemistry, even though enzymes catalyze essentially the same types of reactions.