Studies on the heme environment of oxidized cytochrome b5

Existence of Two Heme B Centers in Cytochromeb 561 from Bovine Adrenal Chromaffin Vesicles as Revealed by a New Purification Procedure and EPR Spectroscopy

“…There were three types of low spin species; two of them showed usual low spin EPR signals (g z ϭ 3.14 and g z ϭ 2.84) arising from the same heme component and were interconvertible depending on pH. A similar transition of EPR signals upon elevation of pH was reported for cytochrome b 5 , in which a neutral form (g z ϭ 3.05, g y ϭ 2.22, g x ϭ 1.41 at pH 6.2) was converted to an alkaline form (g z ϭ 2.76, g y ϭ 2.26, g x ϭ 1.67 at pH 12.0) (16). The cause of this transition is likely either due to deprotonation of one of the axial bisimidazole ligands to form an imidazolate ligation or the imidazole ligand to become strongly hydrogenbonded from a nearby amino acid residue (19).…”

“…Although Burbaev et al reported that the g z ϭ 3.12 species comprised a high potential component with g z ϭ 3.14 and a low potential one with g z ϭ 3.11 (7), our present data showed only one species. The g values of both the g z ϭ 3.14 and g z ϭ 2.84 species are very similar to those of microsomal cytochrome b 5 (g z ϭ 3.05, g y ϭ 2.22, and g x ϭ 1.41) (16), chloroplast cytochrome b 559 (g z ϭ 2.94, g y ϭ 2.27, and g x ϭ 1.54) (17), and cytochrome b of bo-type ubiquinol oxidase (g z ϭ 2.98, g y ϭ 2.26, and g x ϭ 1.45) (18), all of which are known to have bisimidazole ligands. 2 M. Tsubaki, M. Nakayama, and H. Hori, unpublished result.…”

Magnetic circular dichroism studies on microsomal aryl hydrocarbon hydroxylase: Comparison with cytochrome b5 and cytochrome P-450cam

“…Concentrations of cytochrome b 5 were determined according to the published extinction coefficients (Ozols and Strittm~tter, 1964}. The EPR spectrum of this preparation, measured in collaboration with Dr. A. J. Bearden, was essentially identical to that reported by other workers (Bois-Poltoratsky and Ehrenberg, 1967;Ikeda et al, 1974).…”

Distinct Roles of Two Heme Centers for Transmembrane Electron Transfer in Cytochrome b 561 from Bovine Adrenal Chromaffin Vesicles as Revealed by Pulse Radiolysis

“…One of them shows usual low spin signals and is very similar to those of microsomal cytochrome b 5 (25), chloroplast cytochrome b 559 (26), and cytochrome b of bo-type ubiquinol oxidase (27), all of which are known to have bisimidazole ligands. The other species shows a highly anisotropic low spin signal (g z ϭ 3.70) with a lower redox potential and is very similar to those of cytochrome b of the mitochondrial complex III (28,29) and chloroplast cytochrome b 6 (30).…”