Photooxidative and spectral studies on cytochrome c. Conformational changes induced by binding of cardiolipin.

Abstract

Abstract— Binding of cardiolipin to ferrocytochrome c, to form a 4:1 molar complex, results in an approximately sixfold increase of the tryptophan fluorescence emission. Furthermore, appreciable perturbations of the circular dichroism spectrum occur in the Soret and in the far‐ultraviolet regions. The irradiation of the ferrocytochrome–cardiolipin complex at pH 8·8 with visible light leads to the photooxidative modification of histidine‐18, tyrosine‐48 and methionine‐80. Comparison of the above findings with those concerning unbound ferrocytochrome c suggests that the interaction between cardiolipin and ferrocytochrome c provokes a perturbation of the protein conformation, which possibly involves the disruption of the hydrogen bonds linking the aromatic rings of tryptophan‐59 and tyrosine‐48 with one propionic side chain of the heme.