Inhibition of Ribonuclease from Aspergillus saitoi by Nucleosides

抄録

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 orienta-tion 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. pK_i-pH profiles of adenosine, cytidine and guanosine were studied and it was found that the bends concaved side upwards at pH 6.0 observed in the case of pK_m- or pKi-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.