OXYGENATED CYTOCHROME BD FROM ESCHERICHIA-COLI CAN BE CONVERTED INTO THE OXIDIZED FORM BY LIPOPHILIC ELECTRON ACCEPTERS

Cytochrome bd complex as isolated from Escherichia coli under aerobic conditions is in a stable oxygenated form b(558)(3+) b(595)(3+) a(2+)- O-2 characterized by an intense peak at 650 nm in the absolute absorpt ion spectrum. Commonly used oxidants ferricyanide and persulfate have no effect on this oxygenated form, whereas addition of lipophilic elec tron accepters, such as tetrachlorobenzoquinone (BQCl(4))(3) or ferric inium, brings about decay of the heme d oxycomplex and the enzyme tran sition into the fully oxidized form b(558)(3+) b(595)(3+) a(3+) Intera ction of oxygenated cytochrome bd complex with both BQCl(4) and ferric inium is suppressed by pentachlorophenol, an inhibitor of the activity of the enzyme ubiquinol oxidase. It is suggested that redox centers o f cytochrome bd reside in a hydrophobic environment which can prevent their interaction with the hydrophilic oxidants.