Commission on Enzymes

A system based partly on historical names, partly on the substrate, and partly on the type of reaction catalyzed is far from satisfactory. In 1956, the International Union of Biochemistry set up a Commission on Enzymes to consider the classification and nomenclature of enzymes. The Commission presented a report in 1961 whose recommendations for naming and classifying enzymes were subsequently adopted (12). Enzymes are classified on the basis of the reactions they catalyze. Despite its apparent complexities, the system is precise and very descriptive, accommodating existing enzymes and serving as a systematic basis for the naming of new enzymes. AH enzymes are placed in one of the six principal classes. 

In many situations, the actual molar amount of the enzyme is not known. However, its amount can be expressed in terms of the activity observed. The International Commission on Enzymes defines One International Unit of enzyme as the amount that catalyzes the formation of one micromole of product in one minute. (Because enzymes are very sensitive to factors such as pH, temperature, and ionic strength, the conditions of assay must be specified.) Another definition for units of enzyme activity is the katal. One katal is that amount of enzyme catalyzing the conversion of one mole of substrate to product in one second. Thus, one katal equals 6X10 international units. 

Classification of Enzymes. A systematic classification and nomenclature has been established by the Commission on Enzymes of the International Union of Biochemistry (6), which divides enzymes into six general groups ... 

The actual molar concentration of an enzyme in a cell-free extract or purified preparation is seldom known. Only if the enzyme is available in a pure crystalline form, carefully weighed, and dissolved in a solvent can the actual molar concentration be accurately known. It is, however, possible to develop a precise and accurate assay for enzyme activity. Consequently, the amount of a specific enzyme present in solution is most often expressed in units of activity. Three units are in common use, the international unit (IU), the katal, and specific activity. The International Union of Biochemistry Commission on Enzymes has recommended the use of a standard unit, the international unit, or just unit, of enzyme activity. One IU of enzyme corresponds to the amount that catalyzes the transformation of 1 p,mole of substrate to product per minute under specified conditions of pH, temperature, ionic strength, and substrate concentration. If a solution containing... 

The Jhtemationai Union of Biochemistry (TUB) was officially founded in 1953 by an initiative of the British Biochemical Society. At ibis time enzyme standardization was in a chaotic slate, owing to the multiplicity of arbitrarily defined units of enzyme activity and the ilt-dtfned nomenclature. In 1955, the 1UB International Commission on Enzymes was created. This led to an improved enzyme nomoidature, which has been used since 1961, and the definition of the International Unit (LU.) of enzyme activity. 

The International Union of Biochemistry (lUB) established a commission on enzyme nomenclature to adopt a systematic classification and nomenclature of all the existing and yet to be discovered enzymes. This system is based on the substrate and reaction specificity. Although, this International Union of Biochemistry system is complex, it is precise, descriptive and informative. 

International Union of Biochemistry, Report of the Commission on Enzymes (1961), p. 104. Pergamon, Oxford, 1964. 

If the recommendations of the Commission on Enzymes are applied to cellulases, a cellulase unit should be defined as that amount of enzyme... 

The Commission on Enzymes states that, wherever possible, enzyme assays should be based on measurements of initial rates of reaction. A viscometric assay method should be especially suitable for this purpose since the mean molecular weight of a polymer can be rapidly determined by such methods. A useful viscometric method has been worked out by Almin et al. (3,4, 5). 

In accordance with the recommendations of the commission on enzymes of the International Union of Biochemistry (see Nature 188, 464-466, I960 Science 182, 1548-1550, 1960 and Report of the Commission on Enzymes of the International Union of Biochemistry 1961, I.U.B. Symposium Series, Vol. 20, Pergamon Press, London) nicotinamide-adenine dinucleotide (NAD) has been substituted fordiphosphopyridine nucleotide (DPN) nicotinamide-adenine dinuoleotide, reduced form (NADHj), for diphosphopyridiiie nucleotide, reduced form (DPNH) nicotinamide-adenine diuu-cleotide phosphate (NADP), for triphosphopyridine nucleotide (TPN) and nicotinamide-adenine dinucleotide phosphate, reduced form (NADPH2), for triphosphopyridine nucleotide, reduced form (TPNH). 

We shall refer to the systems catalysing secondary translocation reactions as translocators or porters , avoiding the termination ase in conformity with the recommendations of the Commission on Enzyme Nomenclature. Also, in conformity with these recommendations, the systems catalysing group translocation may be called translocases , although, as a rule, the normal enzyme name appears to be more appropriate. 

Because of its role in activating methionine for transmethylation, this enzyme was initially called the methionine-activating enzyme. With the later discovery of enzymes which activate the carboxyl group of methionine and other amino acids for protein synthesis, this term became somewhat confusing. In this chapter, the trivial name methionine adenosyltransferase or adenosyhransferase, will be used in accord with the recommendation of the Commission on Enzymes (Enzyme Nomenclature, American Elsevier, New York, 1965). The enzyme has also been called S-adenosylmethionine synthetase. 

The egg white enzyme has been shown to be an Cfjdo- 3-A -acotyl-D-muramidase but will also act upon e/ido-/3-jV-acetyl-D-glucosaminide linkages in chitin oligosaccharides (Berger and Weiser, 1957). The Enzyme Commission has assigned the number E.C.3.2.1.17 to these enzymes and has recommended (Report of the Commission on Enzymes, 1961) that the name lysozyme be replaced by muramidase or jV-acetylmuramide glycan-hydrolase. 

Report of the Commission on Enzymes, International Union of Biochemistry Symposium, Vol. 20, Pergamon Press, New York, 1961. A discussion and an outline of this Report is given by R. H. S. Thompson, Nature, 193, 1227 (1962). 

About 12 per cent of all known enzymes need a metal co-factor (Commission on Enzymes, 1971). How does the metal help Metals seem often to act as a bridge between the substrate and the protein, which can activate the metal by withdrawing electrons from it. The excess positive charge. 

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