C-terminal destetetrapeptido- and deshexapeptido-RNases A (RA1-120 and RA1-118) were prepared from RNase A by peptic digestion and from RA1-120 by limited carboxypeptidase A action, resp. Both RA1-120 and RA1-118 have definite though significantly weaker hydrolytic activities, especially very weak ribonucleoside 2',3'-cyclophosphate hydrolysis activities, but notably higher synthetic activities than those of natural RNase A. At room temperature, the relative initial velocities of the hydrolysis of uridine 2',3'-cyclophosphate (I) by RNase A, RA1-120, and RA1-118 were 100, 2, and 0.7 resp. The relative synthesis activities of RNase A, RA1-120, and RA1-118 at -15?were 100, 120, and 167, when I and 3'-cytidylate were used as substrates and the yields of UpC enzymically synthesized in 24 h at -15?were compared. Thus, histidine 119 of RNase A mol. is important but not necessary for its hydrolytic activity and is neither important nor necessary for its synthetic activity.

Key words: MOLECULAR STRUCTURE, HYDROLYSIS, ACTIVITY, POLYPEPTIDE, RIBONUCLEASE, NSFC