Standardization of assay procedure and some properties of ribonuclease from Aspergillus candidus

Screening of several fungal cultures resulted in the selection of an isolate of Aspergillus candidus which produced a considerable around of RNa-degrading enzyme in both surface and submerged methods of cultivation. The conditions for the assay of the RNAase were standardized at pH 4.5, 55 degrees C and using 0.25% yeast RNA as substrate. The enzyme was stable at pH 5.2. EDTA was found to activate the enzyme slightly. at temperatures 50-60 degrees C there was considerable loss in enzyme activity which was traced to the presence of a contaminating protease which presumably degraded the RNAase optimally at this temperature. The protease could be preferentially inactivated at or above 75 degrees C. The crude enzyme, in addition to RNAase was found to possess DNAase, nonspecific phosphodiesterase and 3'- and 5'-phosphomonoesterase activities.