title: Spectral evidence for cytochrome o in the brown membrane of Halobacterium halobium.
abstract: The brown membrane domain of Halobacterium halobium is a developmental precursor of the purple membrane and it contains a b-type cytochrome in addition to bacterio-opsin. In this report we provide spectroscopic evidence that the majority of the cytochrome content is a halobacterial cytochrome o. This cytochrome has absorption spectral properties in the oxidized, reduced, and CO liganded states which are characteristic of cytochrome o. The CD spectra show a complex bilobed pattern in the Soret spectral region which reflects the similarity of the heme environment to those of other b-type cytochromes involved in electron transport. We have also demonstrated a positive cooperativity of CO binding which, combined with CD spectral results, suggests two interacting heme moieties per cytochrome o. Size exclusion HPLC of solubilized brown membrane preparations shows a heme b containing protein with an Mr 42,000-46,000. The cytochrome may be easily separated from bacterio-opsin using a hydroxyapatite elution method on Triton X-100 solubilized preparations. The relative ease with which brown membrane disks may be oriented in high optical quality films should make the brown membrane a valuable model system for future spectroscopic investigations of cytochrome o.
authors.affiliation: Department of Microbiology, Ohio State University, Columbus 43210.
authors.forename: S C
authors.initials: SC
authors.lastname: Hartsel
authors.forename: B J
authors.initials: BJ
authors.lastname: Kolodziej
authors.forename: J Y
authors.initials: JY
authors.lastname: Cassim
mesh_terms: D002462:Cell Membrane / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D003573:Cytochrome b Group; D003580:Cytochromes / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D029968:Escherichia coli Proteins; D006217:Halobacterium / Q000032:analysis*; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; C017168:cytochrome bo, E coli