CALORIMETRIC STUDY OF THERMAL-DENATURATION OF SUPEROXIDE-DISMUTASE

The thermal denaturation of superoxide dismutase (SOD) from bovine ery throcytes was studied at various pH values of different buffers and at various concentrations of solutions of two neutral salts by different ial scanning calorimetry. The experiments performed indicate that the PIPES is a buffer non-coordinating with the SOD, and that the binding of the anions studied influences more or less the thermal denaturation of SOD, but the effect on the oxidation form of SOD is more apparent. A new conformer of SOD with lower thermostability was discovered by t he experiments performed in different buffers at certain pH values hig her than the isoelectric point of SOD, or at higher concentrations of neutral salt solutions. The new conformer may be converted irreversibl y into the usual conformer with high thermostability during heating. B ased on the thermodynamic parameters obtained in distilled water and b y thermodynamic analysis using the Ooi's model, it is revealed that th e large enthalpy Delta H-d(c) contributed by the conformational transi tion itself is a factor for SOD to possess very high thermostability.