Enzyme Commission classification scheme

In the following section, enzymes in the EC 2.4 class are presented that catalyze the polymerization of polysaccharides. The Enzyme Commission classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction which is very often used in biocatalytic synthesis. Therefore newer classification systems have been developed, based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation that the enzyme catalyzes etc. [10-15]. The Carbohydrate-Active enZYmes Database [13], which is currently the best database/classification system for carbohydrate active enzymes, uses an amino acid sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g., branching enzyme, sucrases and amylomaltase). Nevertheless we present these enzymes here because they are transferases according to the EC classification. 

Enzyme classification is primarily based on the recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (lUBMB)", and it describes each type of characterized enzyme for which an EC (Enzyme Commission) number has been provided. EC classes define enzyme function based on the reaction, which is catalyzed by the enzyme. The classification scheme is hierarchical, with four levels. There are six broad categories of function at the top of this hierarchy and about 3500 specific reaction types at the bottom. EC classes are expressed... 

All enzymes are named systematically according to a classification scheme designed by the Enzyme Commission (EC) of the International Union of Pure and Applied Chemistry (lUPAC), based on the type of reaction they catalyze. Each enzyme type has a specific, four-integer, EC number and a complex, but unambiguous, name that obviates confusion between enzymes catalyzing similar but not identical reactions. In practice many enzymes are known by a common name that is derived from the name of its principal-specific reactant with the suffix -ase. Some common names do not even have -ase appended, but these tend to be enzymes that were studied in the early days before systematic classification of them had been undertaken (see Examples 5.1-5.3). 

I.U.B. definitions were indicated. Objections were made that the minute is not an S.I. unit. It was proposed to define enzyme activity by a catalytic amount (katal) of a system that catalyzes exactly as many cycles per second of a reaction scheme as there are atoms in 0.012 kg of the pure nuclide 12C. This point of view was adopted and recommended by the commission of Biochemical Nomenclature of I.U.B. in 1972, as appearing in Nomenclature and Classification of Enzymes, together with their units and symbols (revision and extension of recommendations of 1962 and 1964, Elsevier, Amsterdam, 1972). The katal was proposed as a unit of enzymic activity to be used instead of the earlier unit, and this recommendation was approved by the general assembly of the I.U.B. Congress at Stockholm, July 1973. 

---