Conformational transitions and vibronic couplings in acid ferricytochrome c: a resonance Raman study
- 1 May 1979
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 18 (9) , 1656-1660
- https://doi.org/10.1021/bi00576a004
Abstract
Resonance Raman spectral changes in [horse heart] ferricytochrome c as a function of pH between 6.7 and 1.0 are reported and the structural implication is discussed in terms of the core-expansion model advanced by L. D. Spaulding et al. The data are interpreted as indicating that the Fe in high-spin acid ferricytochrome c (at pH 2.0) with 2 water molecules as axial ligands lies in the plane of the porphyrin ring. At pH 1.0 there is a different high-spin form of cytochrome c which has an estimated Fe out-of-plane distance of .apprx. 0.46 .ANG.. The effect of a monovalent anion at pH 2.0 is to produce a thermal spin mixture with predominant low-spin species. Excitation at .apprx. 620 nm in acid cytochrome c (pH 2.0) enhances only 3 depolarized ring vibrations at 1623, 1555, and 764 cm-1. Marked enhancement of depolarized modes relative to polarized and anomalously polarized modes is attributed to the vibronic coupling between porphyrin .pi. .fwdarw. .pi.* and porphyrin .pi. .fwdarw. Fe (d.pi.) charge-transfer states.This publication has 9 references indexed in Scilit:
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