title: Oxidation-reduction potentials and absorption spectra of two b-type cytochromes from the halophilic archaebacterium, Halobacterium halobium.
abstract: The oxidation-reduction midpoint potentials were determined for two b-type cytochromes, which had been solubilized from the membrane of Halobacterium halobium and partially purified. The two b-type cytochromes have oxidation-reduction midpoint potentials of 175 and 7 mV, respectively. These b-type cytochromes could also be resolved by difference absorption spectroscopy, which revealed one b-type cytochrome with absorption maximum (alpha-peak) at 558 nm, reducible by ascorbate-tetramethyl-p-phenylenediamine, and the other with absorption maximum (alpha-peak) at 560 nm, reducible by dithionite. Different substrates such as succinate, NADH, and alpha-glycerophosphate were used to study the b-type cytochromes in situ when bound to the membrane in a functional state. Reducing equivalents from succinate and alpha-glycerophosphate appear to enter the respiratory chain at the 175 mV b-type cytochrome. Cytochrome a3 is spectrophotometrically shown to be present in the membrane of H. halobium.
mesh_terms: D003573:Cytochrome b Group / Q000302:isolation & purification / Q000378:metabolism*; D006217:Halobacterium / Q000378:metabolism*; D007202:Indicators and Reagents; D007700:Kinetics; D010084:Oxidation-Reduction; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D007202:Indicators and Reagents