Spectral evidence for interactions between membrane-bound hemes: Resonance Raman spectra of mitochondrial cytochrome b–c1 complex as a function of redox potential

Abstract

Resonance Raman (RR) spectra of many hemeproteins [l-lo] and metalloporphyrins [ 1 l-161 have been reported since the initial analysis of the scattering enhanced by resonance between the laser frequency and porphyrin rr to n* transitions in cytochrome c by Spiro et al. [17]. Later, more detailed descriptions of the scattering phenomenon in both cytochrome c [ 18-201 and other metalloporphyrins [ 15 ,16,2 l] were presented and correlations were made between RR band frequencies and oxidation and spin states of the iron in various hemeproteins [6,22,23]. Moreover, the proposal was made that because of its high resolution capabilities, RR spectra could be exploited as a probe of interactions between hemes in functioning biological membranes [24] . A model study on the ~-0x0 dimer of tetraphenylporphin indicated that this technique was indeed sensitive to heme aggregation. Our initial work on the succinate cytochrome c reductase showed it to be a fruitful system for RR study for a variety of reasons: (1) RR spectra of isolated cytochromes exhibit well-defined marker bands [7] ; (2) The RR quantum yields of ferrous cytochromes are unusually large (lo-‘) [25] ; (3) The spectroscopic characterization of the RR effect in ferrous cytochromes is highly developed [17-191.