CONVERSION OF ADENOSINE(5')OLIGOPHOSPHO(5') ADENOSINES INTO INOSINE(5')OLIGOPHOSPHO(5')INOSINES BY NONSPECIFIC ADENYLATE DEAMINASE FROM THESNAIL HELIX-POMATIA

Until now, the catabolism of adenosine(5')triphospho(5')adenosine (Ap( 3)A) and adenosine(5')tetraphospho(5')adenosine (Ap(4)A) has been thou ght to commence with either hydrolytic or phosphorolytic cleavage of t heir oligophosphate chains, depending on the organism. Here, we show t hat in the extracts from the retractile 'foot' of the snail Helix poma tia deamination predominates; the adenosine moieties of these and othe r adenosine(5')oligophospho(5')adenosines (Ap(n)As) undergo successive deamination leading, via an inosine(5')oligophospho- (5')adenosine (I p(n)A), to the corresponding inosine(5')oligophospho(5')inosine (Ip(n) I). The reactions are catalyzed by the non-specific adenylate deaminas e described earlier (Stankiewicz, A.J. (1983) Biochem. J. 215, 39-44). We describe TLC and HPLC systems which allow the separation of any of the deaminated derivatives from its parent compound; Ap(2)A, Ap(3)A, Ap(4)A or Ap(5)A. The K-m values for these substrates are 20, 22, 32 a nd 39 mu M, respectively, whereas the K-m for 5'-AMP is 12 mu M Relati ve substrate specificities for these compounds amount to 25, 18, 14, 7 and 100. The enzyme was shown also to deaminate phosphonate and thiop hosphate analogues of Ap(3)A.