Enzyme Commission numbers classification

More than 2000 different enzymes are currently known. A system of classification has been developed that takes into account both their reaction specificity and their substrate specificity. Each enzyme is entered in the Enzyme Catalogue with a four-digit Enzyme Commission number (EC number). The first digit indicates membership of one of the six major classes. The next two indicate subclasses and subsubclasses. The last digit indicates where the enzyme belongs in the subsubclass. For example, lactate dehydrogenase (see pp. 98-101) has the EC number 1.1.1.27 (class 1, oxidoreductases subclass 1.1, CH-OH group as electron donor sub-subclass 1.1.1, NAD(P) " as electron acceptor). 

During natural evolution, a broad variety of enzymes has been developed, which are classified according to the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (IUBMB). Thus, for each type of characterized enzyme an EC (Enzyme Commission) number has been provided (see http // www.expasy.ch/enzyme/). For instance, all hydrolases have EC number 3 and further subdivisions are provided by three additional digits, e.g. all lipases (official name triacylglycerol lipases) have the EC number 3.1.1.3 and are thus distinguished from esterases (official name carboxyl esterases) having the EC number 3.1.1.1. This classification is based on the substrate (and cofactor) specificity of an enzyme only, however often very similar amino acid sequences and also related three-dimensional structures can be observed. 

A-17 According to lUB system enz)mies are grouped in six major classes. Each with sub classes based on the t) e of reaction catalyzed. Systemic classification of enzymes based on numbering system is used. Each enzyme is assigned a code number or EC (enzyme commission number) four-digit classification number and a systematic name, which identifies the reaction catalyzed. 

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... 

Standard abbreviations used in both the biochemical and chemical literature have been employed in the text and are listed in the Biochemical Journal publication, Policy of the Journal and Instructions to Authors issued by the Biochemical Society, London, 1972. Wherever possible enzymes have been named at the first mention by use of the EC (Enzyme Commission) numbers (Recommendations of the International Union of Biochemistry on the nomenclature and classification of Enzymes, Elsevier, Amsterdam, 1965). 

The first Enzyme Commission, in its 1961 report, devised a system for classification of enzymes that also serves as a basis for assigning code numbers to them. Every enzyme has got a 4-digit number EC A.B.C.D. where EC stands for Enzyme Commission with the following properties encoded ... 

All enzymes are named according to a classification system designed by the Enzyme Commission (EC) of the International Union of Pure and Applied Chemistry (IUPAC) and 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 about enzymes catalyzing similar but not identical reactions. In practice, many enzymes are known by a common name, which is usually derived from the name of its principal, specific reactant, with the suffix -ase added. Some common names do not even have -ase appended, but these tend to be enzymes studied and named before systematic classification of enzymes was undertaken. 

Dehydrogenases (or oxidoreductases) constitute the first of six main divisions in the Enzyme Commission classification [ 1 ]. About 300 dehydrogenases that utilize nicotinamide coenzymes are known, and this chapter deals with some of them. The recommended name and EC number designate not a single enzyme protein, but a group of proteins with the same catalytic property [1]. 

To bring some consistency to the classification of enzymes, in 1964 the International Union of Biochemistry established an Enzyme Commission to develop a nomenclature for enzymes. Reactions were divided into six major groups numbered 1 through 6 (Table 8.3). These groups were subdivided and further subdivided, so that a four-digit number preceded by the letters EC for Enzyme Commission could precisely identify all enzymes. 

EC nomenclature for enzymes A classification of ENZYMES according to the Enzyme Commission of the International Union of Biochemistry and Molecular Biology. Enzymes are allocated four numbers, the first of which defines the type of reaction catalyzed the next two define the substrates, and the fourth is a catalogue number. Categories of enzymes are EC 1, oxidoreduc-tases EC 2, transferases EC 3, hydrolases EC 4, lyases EC 5, isomerases EC 6, ligases (Synthetases). 

A large number of different enzymes has been described. Their nomenclature has been rather haphazard, although many enzymes are named by placing -ase after their substrate others are called product synthetase. Enzymes that transfer phosphate from ATP to a substrate are called substrate kinase. An international enzyme commission (EC) has developed a classification number, a systematic name, and a recommended name. Recommended names are widely used, but the EC numbers and systematic names are increasingly used to avoid confusion, often in a footnote. 

Enzyme names. Most enzyme names end in ase. Enzymes usually have both a common name and a systematic classification that includes a name and an Enzyme Commission (EC) number. 

Table 4.1 The Enzyme Commission s system of classification of enzymes and assigning code numbers (Palmer, 2001)...

By the late 1950s, enzyme nomenclature was in confusion. Without any guiding authority, the increase in known enzymes had led to the assignment of misleading or inappropriate names, and in many cases the same enzyme became known by several names while some catalytically different enzymes were identically named. In 1961, the first Enzyme Commission reported a system for enzyme classification and the assignment of code numbers. 

Saier et al. (134-137) have developed a system of transporter classification (T.C. number) analogous to the Lnzyme Commission (L.C. number) system for uniquely identifying enzymes. Transporters are organized as follows ... 

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