title: Four different b-type cytochromes in the halophilic archaebacterium, Halobacterium halobium.
abstract: The halophilic archaebacterium, Halobacterium halobium has been found to contain four different b-type cytochromes. The four components were recognized by their potentiometric characteristics in situ in their functional environment in the membrane of H. halobium. Oxidation-reduction midpoint potentials of these four b-type cytochromes were determined to be +261, +160, +30, and -153 mV, respectively. We also demonstrate that the pathway involved in the transport of reducing equivalents from succinate to oxygen proceeds through the b-type cytochromes with oxidation-reduction midpoint potentials of +261 and +161 mV. The cytochrome with oxidation-reduction midpoint potential of -153 mV was not substrate reducible by NADH but was chemically reducible by dithionite. Antimycin inhibits reduction of b-type cytochrome in the succinate pathway, but has no effect on b-type cytochrome reduction when reducing equivalents are provided by NADH. The carbon monoxide difference spectrum of H. halobium membranes shows at least one carbon monoxide-binding b-type cytochrome, indicating a terminal oxidase. A scheme for electron transport in H.halobium involving the b-type cytochromes and terminal oxidase is suggested.
authors.affiliation: Department of Biochemistry, University of Stockholm, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Hallberg Gradin
authors.forename: A
authors.initials: A
authors.lastname: Colmsjö
mesh_terms: D000968:Antimycin A / Q000031:analogs & derivatives / Q000494:pharmacology; D002248:Carbon Monoxide; D002462:Cell Membrane / Q000032:analysis; D003573:Cytochrome b Group / Q000032:analysis* / Q000378:metabolism; D004579:Electron Transport; D006217:Halobacterium / Q000032:analysis*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D011199:Potentiometry; D013053:Spectrophotometry; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid
chemical_list: D003573:Cytochrome b Group; D013386:Succinates; D009243:NAD; C032456:antimycin; D000968:Antimycin A; D002248:Carbon Monoxide; D019802:Succinic Acid; D010100:Oxygen