ENZYMES 



153 



be divided into several types according to the nature of the donor system 

 and the transferable group. The general type of transfer reaction and the 

 particular case where water is the acceptor can be represented by the 

 following two schemes of reaction : 



R_X+HE ^ R— E+XH R-X+HE ^ R— E+XH 



f ' \ 



YH H OH 



R— Y+HE R— OH+HE 



in which R — X is the substrate (donor system), R is the transferable group, 

 Y is the acceptor system and E is the enzyme. 



Hydrolases catalyse the transfer of transferable groups to water. If 

 another acceptor is present, in sufficient quantities and in the presence of 

 the specific enzyme for the activation and transfer of the group to this 

 other acceptor, then this reaction will compete with the hydrolysis. 



The donor system varies according to the various types of hydrolases 

 and the transferable group may be attached by a peptide bond, oside bond, 

 ester bond, amine linkage, amide bond or an amidine linkage. 



In all living beings, as a rule, seven types of hydrolases are recognized. 



O 



O 



(a) Peptidases 



RC— NHR' + H.,0 ^ RC-OH + NH.R 



(b) Carbohydrases R' — O— R' + HoO ^ R'OH + R'OH 



(R^ and R^ are sugar residues or osides, they can be identical.) 

 O O 



II II 



(c) Esterases R'— C— OR' + H,0 ^ R^C— OH + R'OH 



(d) Phosphatases R— O— PO3H2 + H2O ^ ROH + H3PO4 



(e) Deaminases 



R— NH2 + H2O ^ ROH + NH3 

 O O 



(f) Deamidases R— C— NH^ + H2O ^ R— C— OH + NH3 



NH 



(g) Deamidi- II 



nases R— NH— C— NHo + H2O ^ R— NHo + H2NCONH2 



