158 UNITY AND DIVERSITY IN BIOCHEMISTRY 



(g) Deamidinases 



These enzymes catalyse the hydrolysis of amidine bonds. The most 

 well-known of them is arginase catalysing the hydrolysis of arginine to 

 ornithine and urea. Its molecule contains manganese. 



B. Phosphorylases 



They catalyse the transfer of a transferable group, not to water, but to 

 phosphoric acid. They are transglucosidases whose acceptor is phosphoric 

 acid. The general formula for the transfer reaction is as follows : 



(C6Hio05)„ + H3PO4 ^ CcHnOs— OPO3H2 + (CeHaoOs)™-! 



Glucose- 1 -phosphate 



The phosphorylases are everywhere present in the biosphere. An enzyme 

 of this type (phosphorylase-a) has been obtained crystalline from rabbit 

 muscle. In the presence of an excess of orthophosphate the reaction occurs 

 in the direction of phosphorolysis, whilst in the absence of orthophosphate 

 or in the presence of an excess of glucose- 1 -phosphate, the synthesis of 

 amylose takes place. The enzyme is also called glucose- 1 -phosphate ->- 

 amylose-transglucosidase. 



From various microbial sources have been isolated a sucrose phos- 

 phorylase (sucrose -> orthophosphate transglucosidase) and a maltose 

 phosphorylase (maltose -> orthophosphate transglucosidase). 



