Abstract
An enzyme preparation has been purified about forty fold from a strain of Aspergillus oryzae. This preparation catalyzes the hydrolytic cleavage of inosine, guanosine, 5'-IMP, and 5'-GMP to the corresponding bases (hypoxanthine and guanine) and ribose or its 5-phosphate. No change is observed in the relative rates of hydrolysis of these four substrates with purification, indicating that a single enzyme “ribosidase”, which cleaves specifically the ribosidic linkages of 6-hydroxypurine ribonucleosides (inosine and guanosine) or their 5'-phosphates, does exist in Aspergillus oryzae. It has been found that 5'-AMP, 5'-CMP, 5'-UMP, adenosine, cytidine, uridine, and various 3'- or 2'-mononucleotides are not cleaved by the enzyme. No evidence for the requirement of ATP, P, or PP has been found. This enzyme is rather thermostable in the pH range from 5.0 to 6.5. The optimum conditions for activity are at about 45°C and pH 4.0.
