Detection of a bulk water structure related conformational change in horse heart cytochrome c in Cl- -H2O solutions utilizing spectrofluoroelectrochemical techniques

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 degrees C of the ratio is sigmoidal in nature, indicative of a conformational transition with the midpoint being 43 degrees 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 E0' 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 degrees C and it is postulated that the conformational changes of cyt c are the result of the behavior of the bulk water structure.