INTERMEDIATE STAGES IN THERMALLY INDUCED TRANSCONFORMATION REACTIONS OF BOVINE PANCREATIC RIBONUCLEASE A

The nature of the thermally induced unfolding reactions of bovine pancreatic RNase was studied using proteolytic enzymes as conformational probes. The initial rates of proteolysis, as catalyzed by aminopeptidase, trypsin, chymotrypsin, and carboxypeptidase, were studied both with RNase and performic acid oxidized RNase as substrates. The latter protein served as a control substrate to take account of the effect of temperature on the proteases. The temperature range studied was between 30[degree] and 60[degree] at pH 8 in 0.1 [image] NaCl. The conformation of RNase changes in a gradual manner with increasing temperature and that some central regions become disordered at lower temperatures than does either end of the molecule. Concomitant optical rotatory dispersion studies also indicate that the thermally induced conformation changes of RNase take place in a gradual rather than a 2-step process.