Enzyme Commission classification

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]. 

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. 

TABLE 5.3 Some examples of enzyme commission classification and coding... 

Systematic Classification of Enzymes According to the Enzyme Commission ... 

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 ... 

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). 

For biotechnological purposes enzymes are used as biocatalysts to accelerate a desired reaction to its end point. As catalysts enzymes can catalyze a reaction in both directions. Unfortunately the name of an enzyme given by the Enzyme Commission for the classification of enzymes, and biochemistiy text books, stresses the function as a catalyst in one direction only Hydrolases, a group of enzymes of considerable importance in... 

The International Union of Biochemistry has recommended that enzymes have three names, namely a systematic name, which shows the reaction being catalysed and the type of reaction based on the classification in Table A7.1, a recommended trivial name and a four figure Enzyme Commission code (EC code). Nearly all systematic and trivial enzyme names have the suffix -ase. Systematic names show, often in semi-chemical equation form, the conversion the enzyme promotes and the class of the enzyme. Trivial names are usually based on the function of the enzyme but may also include or be based on the name of the substrate. However, some trivial names in current use are historical and bear no relationship to the action of the enzyme or its substrate, for example, pepsin and trypsin are the names commonly used for two enzymes that catalyse the breakdown of proteins during digestion. The Enzyme Commission s code is unique for each enzyme. It is based on the classification in Table A7.1 but further subdivides each class of enzyme according to how it functions. The full code is... 

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. 

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. 

The classic enzyme commission (EC) classification for GTs is on the basis of their donor and acceptor specihcity as well as the product formed. Currently, 295 entries are in this database (http //www.chem.qmul.ac.uk/iubmb/). The distinction between these enzymes is noted by their ability to catalyze the transfer of hexoses (EC 2.4.l.y, hexosyltransferases), pentoses (EC 2.4.2.y, pentosyltransferases), or other glycosyl groups (2.4.99.y, sialyltransferases). This classification is restricted to enzymes that are fully characterized, and it can be problematic for enzymes that act on several distinct acceptors but at different rates. It also does not take into account the origin of the enzyme or its three-dimensional stmcture. 

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. 

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. 

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). 

Table 12.5-1. Principles of peptidase classification according to the Enzyme Commission (E.C.) of the International Union of Biochemistry and Molecular Biology 16 ...

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. 

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... 

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