SUMMARY: Cells from oxygen-limited cultures of NCIB 6428 contained cytochrome , a 596 nm absorbance (in reduced oxidized difference spectra at room temperature) similar to cytochrome , and -type cytochromes, including a cytochrome -like pigment. Oxygen-sufficient cells lacked the and -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 -like species, but not cytochromes or . When a similar suspension, but to which O 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 (FeO or FeO ) complex of cytochrome oxidase 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 -like haemoprotein and (ii) cytochrome oxidation. Laser photolysis of the cytochrome -CO complex at −81°C in the presence of oxygen suggested that oxidation of cytochrome preceded that of cytochrome(s) It is proposed that, in this strain of , a cytochrome ,-like pigment mediates electron transfer from cytochrome(s) to cytochrome oxidase , but that cytochrome is not itself an oxidase.


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