title: Heme centers of Rhodothermus marinus respiratory chain. Characterization of its cbb3 oxidase.
abstract: Rhodothermus (R.) marinus, a thermohalophilic gram-negative, and strict aerobic bacterium, has a rather distinct respiratory chain, containing a caa3 terminal oxidase, a novel cytochrome bc complex and a HiPIP, which is an electron carrier between this complex and a terminal oxidase (Pereira et al (1999a, c). To further elucidate this unusual respiratory system, its membrane-bound heme centers were characterized by visible and EPR spectroscopies as well as by redox potentiometry. Rhodothermus marinus contains mostly B- and C-type hemes; a small amount of A-type heme is also detected. The heme centers have relatively low reduction potentials, ranging from ca. +250 to -60 mV, at pH 7. A Rieske-type center was not detected, suggesting the absence of a canonical complex III. The major terminal oxidase expressed by R. marinus is a cbb3-type oxidase. Its presence is in agreement with molecular biology studies, which reveal the existence of a gene encoding for a FixN-type oxidase. The oxidase was partially purified and appears to have five subunits, with apparent molecular masses of 64, 57, 36, 26 (C-type heme subunit), and 13 kDa. It contains two low-spin heme C centers, one high-, and one low-spin heme B centers. A full description of the equilibrium redox behavior of the heme centers was obtained for a cbb3 oxidase for the first time. The optical spectrum for each heme center and the corresponding reduction potentials were determined at pH 7: + 195 (heme C), +120 (heme B), -50 (heme C), and -50 mV (heme B3).
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
authors.forename: M M
authors.initials: MM
authors.lastname: Pereira
authors.forename: J N
authors.initials: JN
authors.lastname: Carita
authors.forename: R
authors.initials: R
authors.lastname: Anglin
authors.forename: M
authors.initials: M
authors.lastname: Saraste
authors.forename: M
authors.initials: M
authors.lastname: Teixeira
mesh_terms: D000595:Amino Acid Sequence; D001420:Bacteria, Aerobic / Q000201:enzymology* / Q000235:genetics; D002457:Cell Extracts; D002462:Cell Membrane / Q000201:enzymology; D003576:Electron Transport Complex IV / Q000235:genetics*; D005798:Genes, Bacterial; D006090:Gram-Negative Bacteria / Q000201:enzymology* / Q000235:genetics; D006418:Heme / Q000235:genetics*; D013058:Mass Spectrometry / Q000379:methods; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
chemical_list: D002457:Cell Extracts; D006418:Heme; C414443:cbb3 oxidase; D003576:Electron Transport Complex IV