INHIBITION OF RIBONUCLEASE FROM ASPERGILLUS SAITOI BY NUCLEOSIDES

1.Ribonuclease from Aspergillus saitoi [RNase M, EC 2.7.7.17] was found to be inhibited competitively by various nucleosides. Among four common ribonucleosides, the inhibitory effect was in the following order, A>C>G>U.2. When the base was the same, deoxyribonucleoside was found to be less effective than ribonucleoside. It was suggested that the RNase M bound with 2'-OH group of ribonucleoside in some way.3. α-Anomers of adenosine and guanosine were less effective than the natural β-anomers. This indicates that the RNase M requires the nucleoside the proper orientation of the sugar 2'-OH or 3'-OH and base moiety.4. L-β-Cytidine-5'-phosphate was less effective than D-β-cytidine-5'-phosphate(CMP). From this result, it was suggested that the RNase M requires nucleosides the proper spacial relationship among base, 2'-OH and ether oxygen.5. When mixed with nucleosides, the RNase M gave similar difference spectra to those observed by mixing with nucleotides.6. pKt-pH profiles of adenosine, cytidine and guanosine were studied and it was found that the bends concaved side upwards at pH6.0 observed in the case of pKm- or pKt-pH profile of nucleotide were not observed.7. Inactivation of the RNase M by iodoacetate was protected by the presence of adenosine, but not by photooxidation.8. From the results obtained here, possible mode of binding of nucleosides with the RNase M was discussed. © 1969 BY THE JOURNAL OF BIOCHEMISTRY.