Abstract
The thermal denaturation of microbial Ribonuclease T1 (RNAase T1) as a function ofpH, was studied by means of DSC microcalorimetry. The midpoint denaturation temperatures, enthalpy changes and heat capacity changes of Ribonuclease T1 were compared with those obtained for pancreatic Ribonuclease A (RNAase A). It was found that the microbial T1 protein undergoes a more complex conformational transition than the simple two-state transition shown by Ribonuclease A. The hypothesis of the presence of a ‘molten globule’ form is discussed. The conformational stability of RNAase T1 is lower than that of RNAase A at highpH values. Indeed, the maximum stability of RNAase T1 occurs atpH ≈ 5, whereas that of RNAase A occurs atpH ≈ 8. AtpH=3.7 an irreversible aggregation phenomenon was indicated by the existence of a reproducible exothermic peak. The conformational transition of RNAase T1 is reversible in the range ofpH 4.5–7.0, whereas it becomes irreversible atpH≥8.0 as for RNAase A.
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