PURIFICATION, SOME PROPERTIES, AND PRIMARY STRUCTURE OF A BASE NONSPECIFIC RIBONUCLEASE FROM OYSTER (CRUSSDSTREA-GRIGUS)

A ribonuclease (RNase Oy) was purified to homogeneity on SDS-PAGE from the homogenate of oyster (Crussdstrea grigus). The apparent molecular weight estimated from SDS-PAGE was ca. 28 kDa. The pH optimum of the RNase was 5.0. The RNase released mononucleotides from RNA in the orde r of 3'-GMP, 3'-AMP, and 3'-UMP. The complete amino acid sequence of R Nase Oy was determined, mostly by analyzing the peptides generated by BrCN cleavage or digestion by lysylendopeptidase, staphylococcal V8 pr otease, and alpha-chymotrypsin. The molecular weight of the protein mo iety of RNase Oy deduced from the sequence was 24,359. The sequence of RNase Oy contained two typical histidine residues in segments common to the active site of RNase T-2 family enzymes. The locations of six h alf cystine residues among eight were almost superimposable on those o f four known plant RNases of RNase T-2 family. The sequence homology b etween RNase Oy and five fungal and four plant RNases amount, to 43-56 amino acid residues. The amino acid sequence of the N-terminal part o f RNase Oy is more similar to those of plant RNases than to those of f ungal RNases. This RNase is the first RNase T-2 family RNase from moll usc whose primary structure has been elucidated.