52 BACTERIOLOGICAL CHEMISTRY 



in common the possibility of undergoing the change which 

 the particular enzjrme effects. 



The Classification of Enzymes. — Since, for the most 

 part, enzymes are not well-defined chemical entities 

 they cannot be named as compounds in accordance with 

 the normal chemical usage, but they are named by what 

 they do, their specificity being made the basis of the usual 

 classification and nomenclature. An enzyme is normally 

 named by affixing the syllable " -ase " to the root of the 

 name of the substrate on which it acts or to the type of 

 reaction which it catalyses. For example, the enzyme 

 which hydrolyses invert sugar is called invertase ; enzymes 

 which break up esters are known as esterases, those acting 

 on proteins are proteases, those on carbohydrates are 

 carbohydrases. Enzymes influencing oxidation and re- 

 duction reactions are called oxidases and reductases 

 respectively. Some names, such as pepsin and trypsin, 

 given to enzymes in the past and which have become 

 generally accepted are still retained, although they do 

 not conform to the general system. 



For a number of enzymes, particularly those involved 

 in respiratory processes, the nature of the prosthetic 

 group is known, and they are sometimes classified on this 

 basis. Thus catalase and peroxidases are porphyrin- 

 protein enzymes because their prosthetic groups contain 

 iron porphyrin complexes. The pjn^idino -protein enzymes 

 are those which involve the di- or tri-phosphopyridine 

 nucleotides, co -enzymes I and II, attached to specific 

 protein carriers. The flavoprotein enzymes, in which 

 the prosthetic group is riboflavin (see p. 42) are con- 

 cerned with the oxidation and reduction cycles of the 

 CO -enzymes I and II. The copper-protein enzymes, 

 such as tyrosinase and ascorbic oxidase, contain haemocy- 

 anin. Carboxylase, which carries aneurin as its prosthetic 

 group, is a thiamino -protein enzyme. 



There are two large groups of enzymes important in 

 the chemistry of micro-organisms. The Hydrolases 



