Identification of heme axial ligands of cytochrome c′ from Alcaligenes sp. N.C.I.B. 11015

Abstract

The spectral properties of both ferric and ferrous sytochromes c′ from Alcaligenes sp. N.C.I.B. 11015 are reported. The EPR spectra at 77 K and the electronic. resonance Raman, CD and MCD spectra at room temperature have been compared with those of the other cytochromes c′ and various hemoproteins. In the ferrous form, all the spectral results at physiological pH strongly indicated that the heme iron(II) is in a high-spin state. In the ferric form, the EPR and electronic absorption spectra were markedly dependent upon pH. EPR and electronic spectral results suggested that the ground state of heme iron(III) at physiological pH consists of a quantum mechanical admixture of an intermediate-spin and a high-spin state. Under highly alkaline conditions, identification of the axial ligands of heme iron(III) was attempted by crystal field analysis of the low-spin EPR g values. Upon the addition of sodium dodecyl sulfate to ferric and ferrous cytochrome c′, the low-spin type spectra were induced. The heme environment of this low-spin species is also discussed.