title: Acidic cytochrome c6 of unicellular cyanobacteria is an indispensable and kinetically competent electron donor to cytochrome oxidase in plasma and thylakoid membranes.
abstract: Cytochromes c6 from three cyanobacteria were tested as substrates for membranous cyt. c oxidase(aa3) of Anacystis and Synechocystis using intact spheroplasts or isolated plasma(CM) and thylakoid(ICM) membranes. Neither spheroplasts nor CM/ICM gave significant O2 uptake rates with NADH without added cyt. c. Horse cyt. c (at low ionic strength) or cyt. c6 from Anacystis, Synechocystis or Microcystis (at high ionic strength) supported substantial HCN- & CO-sensitive NADH oxidase activity, consistent with in vivo O2 uptake. Cyanobacterial respiratory electron transport involves NADH dehydrogenase(fpN), plastoquinone, cyt. b/c(f), cyt. c6 & cyt. aa3, in both CM & ICM. In ICM, fpN and cyt. aa3 are functionally replaced in the light by PS II and PS I, respectively. In both membranes, cyt. c6 is an obligatory electron donor to cyt. aa3 &/or to P700. Respiratory action of acidic cyt. c6 (in unicellular species) may be unmasked only under conditions of elevated ionic strength.
authors.affiliation: Institute of Physical Chemistry, University of Vienna, Austria.
authors.forename: D
authors.initials: D
authors.lastname: Moser
authors.forename: P
authors.initials: P
authors.lastname: Nicholls
authors.forename: M
authors.initials: M
authors.lastname: Wastyn
authors.forename: G
authors.initials: G
authors.lastname: Peschek
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002736:Chloroplasts / Q000201:enzymology* / Q000648:ultrastructure; D000458:Cyanobacteria / Q000201:enzymology*; D003580:Cytochromes / Q000378:metabolism*; D045348:Cytochromes f; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D013057:Spectrum Analysis
chemical_list: D003580:Cytochromes; D045348:Cytochromes f; D003576:Electron Transport Complex IV