PROTEOLYTIC SUSCEPTIBILITY AND METHIONINE MODIFICATION OF MONODEAMIDATED RIBONUCLEASE A

The susceptibility of a monodeamidated RNAaseA (RNAaseAa₁) towards carboxypeptidaseA, α-chymotrypsin and pepsin has been studied. Similar to RNAaseA, the C-terminal of RNAaseAa₁ is not available for carboxypeptidase A hydrolysis. The thermal stability of RNAaseAa₁ as probed through chymotryptic digestion is found to be less than that of RNAaseA. Preliminary chromatographic analysis of the digested material, however, suggests that the nature of thermal transition might be the same in the two proteins. Pepsin inactivates RNAaseAa₁ more slowly than does RNAaseA. Accordingly, less peptide bonds, almost half that of RNAaseA, are cleaved by pepsin in RNAaseAa_1. The accumulation of RNAase-P type intermediates is not evident during peptic digestion of RNAaseAa_1. Reaction with O-benzoquinone at low pH shows that methionines of the deamidated protein seem to have higher reactivities. These observations indicate a different structure for RNAaseAa₁ at elevated temperature and low pH.