Hydrolytic cleavage of purine ribonucleosides by extracts of Aspergillus terricola.

Cell-free extracts of nitrate-grown Aspergillus terricola could catalyze the hydrolytic cleavage of the N-glycosidic bond of adenosine, guanosine and inosine optimally at pH 4 and 50 degrees C. Incubation of the extracts at 60 degrees C for 60 minutes caused about 86%, 67% and 54% loss of activity respectively. The similarities between the pH or the temperatures profiles indicate that the hydrolytic cleavage of these purine ribonucleosides might be effected by one hydrolase. The results obtained indicate the absence of evidence for the involvement of an SH group(s) in the catalytic site. CoSO4 and CuSO4 showed a remarkable inhibiting effect on enzyme activity. The apparent Km values of the ribonucleoside hydrolase for adenosine, guanosine and inosine were calculated from Lineweaver--Burk plots and found to be 20, 22.2 and 10 x 10(-3)M respectively.