Interactions of cytochromec with phospholipid membranes

Abstract

Cytochromec can be bound to mixed cardiolipin-lecithin liquid crystals so that it cannot be removed by repeated washings with solutions of high ionic strength. The oxidized and reduced spectra of this cytochromec show no detectable differences from those for soluble cytochromec. Unlike soluble cytochromec, however, some 90% of the bound cytochromec is not reduced by ascorbate, and it is only slowly reduced by dithionite. The addition of redox dyes causes complete and immediate reduction in the presence of ascorbate or dithionite. It is suggested that this is because the dyes possess some degree of lipid solubility and are able to penetrate the phospholipid membrane barriers separating cytochromec from the bulk solution. The addition of detergents, such as Triton X-100, also promotes reduction of the bound cytochromec by ascorbate. A small change in the standard potential from, 273 mV for soluble cytochromec to 225 mV for the bound cytochromec was found. The bound cytochromec reacts readily with potassium cyanide to form the normal cyanide-ferricytochromec complex, differing in the rate of formation from soluble cytochromec only at alkaline pH values. The relationship of these findings to work on the membrane-bound cytochromec in mitochondria and submitochondrial particles is discussed.

Low-temperature electron paramagnetic resonance study of the ferricytochrome c-cardiolipin complex

“…As an example of the correlation proposed by Schejter and Eaton (1984), we note that the redox potential for cytochrome bs with an imidazole as an axial ligand is 20 mV (Kawai et al, 1963), while that of normal cytochrome c with a methionine axial ligand is 260 mV (Kimelberg & Lee, 1970). The charge transfer band frequencies (Schejter & Eaton, 1984) for the imidazolocytochrome c are greater (6580 and 7840 cm"1) than those of cytochrome c (5780 and 6825 cm"1), as are the tetragonal and rhombic crystal field splitting parameters derived from the EPR g factors of the imidazole species.…”

Reduction and activity of cytochrome c in the cytochrome c-cytochrome aa3 complex

“…1 and 2) and in the initial stages in the anaerobic system ( Figs. 3 and 4) cytochrome a always behaves as if it had a more positive redox potential than bound cytochrome c (+23OmV; Kimelberg & Lee, 1970). Quasi-equilibrium (Keq 5; Fig.…”

1H-n.m.r. evaluation of the ferricytochrome c-cardiolipin interaction. Effect of superoxide radicals

“…study (Vincent et al, 1987) of ferricytochrome c, revealing a shift of the g.-value from 1.25 to 1.54 in the protein-lipid complex, from which it was concluded that a conformational change of the haem group occurs. This finding was suggested to account for the observed fall in redox potential from 260 mV to 220 mV following formation of the complex between cytochrome c and cardiolipin (Kimelberg & Lee, 1970).…”