The Cytochromes of Acetobacter pasteurianus NCIB 6428. Evidence of a Role for a Cytochrome a1-like Haemoprotein in Electron Transfer to Cytochrome Oxidase d

Abstract

SUMMARY: Cells from oxygen-limited cultures of Acetobacter pasteurianus NCIB 6428 contained cytochrome d, a 596 nm absorbance (in reduced minus oxidized difference spectra at room temperature) similar to cytochrome a 1, and b-type cytochromes, including a cytochrome o-like pigment. Oxygen-sufficient cells lacked the d and a 1-like components. Pyridine haemochrome spectra suggested the presence of haem a. Photolysis with white light at −126°C of an anoxic suspension of reduced oxygen-limited cells, into which CO had been bubbled, elicited a photodissociation spectrum that revealed the cytochrome o-like species, but not cytochromes d or a 1. When a similar suspension, but to which O2 had been added at −23°C, was photolysed at −126 to −132°C, using white light or irradiation with a He-Ne laser, an additional, intense absorbance at 648 nm (relative to the CO-liganded, reduced form) was observed, attributable to an oxygenated (Fe2+O2 or Fe3+O2 -) complex of cytochrome oxidase d. Photolysis at progressively warmer temperatures, or successive scans of a sample photolysed at −91°C, revealed (i) increasing depth of a trough (relative to the CO-liganded, reduced form) at 598 nm attributed to the a 1-like haemoprotein and (ii) cytochrome b oxidation. Laser photolysis of the cytochrome d-CO complex at −81°C in the presence of oxygen suggested that oxidation of cytochrome a 1 preceded that of cytochrome(s) b. It is proposed that, in this strain of Acetobacter, a cytochrome a 1,-like pigment mediates electron transfer from cytochrome(s) b to cytochrome oxidase d, but that cytochrome a 1 is not itself an oxidase.