Probing a complex of cytochromecand cardiolipin by magnetic circular dichroism spectroscopy: Implications for the initial events in apoptosis

Justin M. Bradley, Gary Silkstone, Michael T. Wilson, Myles R. Cheesman, Julea N. Butt

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Oxidation of cardiolipin (CL) by its complex with cytochrome c (cyt c) plays a crucial role in triggering apoptosis. Through a combination of magnetic circular dichroism spectroscopy and potentiometric titrations, we show that both the ferric and ferrous forms of the heme group of a CL:cyt c complex exist as multiple conformers at a physiologically relevant pH of 7.4. For the ferric state, these conformers are His/Lys- and His/OH–-ligated. The ferrous state is predominantly high-spin and, most likely, His/–. Interconversion of the ferric and ferrous conformers is described by a single midpoint potential of -80 ± 9 mV vs SHE. These results suggest that CL oxidation in mitochondria could occur by the reaction of molecular oxygen with the ferrous CL:cyt c complex in addition to the well-described reaction of peroxides with the ferric form.
Original languageEnglish
Pages (from-to)19676-19679
Number of pages4
JournalJournal of the American Chemical Society
Issue number49
Publication statusPublished - 14 Nov 2011

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