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J. Biochem, 1980, Vol. 87, No. 4 1111-1117
© 1980 Japanese Biochemical Society

research-article

Calorimetric Study of the Reduction of the Disulfide Bonds in Insulin1

Harumi FUKADA and Katsutada TAKAHASHI

Laboratory of Biophysical Chemistry, College of Agriculture, University of Osaka Prefecture Sakai, Osaka 591

Calorimetric measurement was made on the reduction of the three disulfide bonds of insulin by dithiothreitol (DTT). The reaction was performed at 298 K in three different buffer solutions of pH 9.6. The observed heat changes were corrected for the enthalpy of proton release from the buffer components and the net heat of reaction of insulin with DTT was determined to be {Delta}Ho=51.5±1.4 kJ(mol insulin)–1. By subtracting the enthalpy of DTT oxidation (Fukada, H. & Takahashi, K. (1980) J. Biochem. 87, 1105–1110), the standard enthalpy of reduction of insulin was found to be {Delta}H = 78.8±7.9 kJ(mol insulin)–1. Using the enthalpy change for reduction of random-coil proteins by dithioerythritol (Johnson, R.E., Adams, P., & Rupley, J.A. (1978) Biochemistry 17, 1479–1484), the enthalpy change associated with the conformational change of insulin alone was evaluated to be {Delta}H = 74±2 kJ(mol insulin)–1 (or 13 J(g protein)–1), a value very similar to that observed for the denaturation of other globular proteins.

1Presented in part at the 34th Annual U.S. Calorimetry Conference, Kent, Ohio, July 1979


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