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Keywords:

  • amino acid substitution;
  • deamidation;
  • 65–72 disulfide loop;
  • monodeamidated derivatives;
  • refolding;
  • 67–74 region;
  • RNase A

The influence of chemical mutation featuring the selective conversion of asparagine or glutamine to aspartic or glutamic acid, respectively, on the kinetics of refolding of reduced RNase has been studied. The monodeamidated derivatives of RNase A, viz. RNase Aa1a, Aa1b, and Aa1c having their deamidations in the region 67–74, were found to regain nearly their original enzymatic activity. However, a marked difference in the kinetics of refolding is seen, the order of regain of enzymic activity being RNase A > Aa1c Aa1a > Aa1b. The similarities in the distinct elution positions on Amberlite XE-64, gel electrophoretic mobilities, and u.v. spectra of reoxidized and native derivatives indicated that the native structures are formed. The slower rate of reappearance of enzymic activity in the case of the monodeamidated derivatives appears to result from altered interactions in the early stages of refolding. The roles of some amino acid residues of the 67–74 region in the pathway of refolding of RNase A are discussed.