Biphasic reductive unfolding of ribonuclease A is temperature dependent.

The kinetics of the reversible thermal unfolding, irreversible thermal unfolding, and reductive unfolding processes of bovine pancreatic ribonuclease A (RNase A) were investigated in NaCl/Pi solutions. Image parameters including Shannon entropy, Hamming distance, mutual information and correlation coefficient were used in the analysis of the CD and 1D NMR spectra. The irreversible thermal unfolding transition of RNase A was not a cooperative process, pretransitional structure changes occur before the main thermal denaturation. Different dithiothreitol (dithiothreitolred) concentration dependencies were observed between 303 and 313 K during denaturation induced by a small amount of reductive reagent. The protein selectively follows a major unfolding kinetics pathway with the selectivity can be altered by temperature and reductive reagent concentration. Two possible explanations of the selectivity mechanism were discussed.