Information about its active stie and mechanism of action has been studied at great length. When RNAse is treated with subtilisin, the peptide bond between 20 and 21 residues is hydrolysed forming a fragment containing 20 residues (1 to 20),called S-peptide. Residues 21 to 124,called S-protein, do not show any catalytic activity ,but when the S-peptide and S-protein are mixed, catalytic activity is restored. Experiments have shown the either histidine (12) or Methionine (13) or both, play a key role in the catalytic activity of RNAse. There are several mechanisms of catalysis which have been proposed for this enzyme.