Abstract
Utilizing the ratio of the fluorescence intensities of the reduced and oxidized forms of horse heart cytochrome c (cyt c), it is possible to monitor conformational changes of the protein upon reduction. The temperature dependence from 25 to 50°C of the ratio is sigmoidal in nature, indicative of a conformational transition with the midpoint being 43°C in 0.10 m NaCl, 0.10 m PO4 buffer, pH 7.0, solution. This transition is consistent with the previously postulated biphasic model used to explain the nonlinearity in EO′ vs T in Cl− −H2O solutions [C. W. Anderson, H. B. Halsall, W. R. Heineman, and G. P. Kreishman (1977)Biochem. Biophys. Res. Commun.76, 339–344]. In addition, the chemical shift of the bulk water proton in tetramethylammonium chloride solution shows a nonlinearity at 42°C and it is postulated that the conformational changes of cyt c are the result of the behavior of the bulk water structure.
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