Kinetics of electron transfer between plastocyanin and the soluble CuA domain of cyanobacterial cytochrome c oxidase

• Published in: FEMS microbiology letters Vol. 239; no. 2; pp. 301 - 307
• Main Authors: Paumann, Martina, Bernroitner, Margit, Lubura, Borjana, Peer, Michael, Jakopitsch, Christa, Furtmüller, Paul G., Peschek, Günter A., Obinger, Christian
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.10.2004; Blackwell; Oxford University Press
• Subjects: Bacteriology; Biological and medical sciences; Copper; Copper - chemistry; CuA domain; Cyanobacteria; Cyanobacteria - enzymology; Cyanobacterium; Cytochrome; Cytochrome oxidase; Cytochrome-c oxidase; Cytochromes; Domains; E coli; Electron transfer; Electron Transport; Electron Transport Complex IV - chemistry; Electrons; Fundamental and applied biological sciences. Psychology; Kinetics; Microbiology; Oxidase; Permeability, membrane transport, intracellular transport; Photosynthesis; Physiology; Plastocyanin; Plastocyanin - chemistry; Proteins; Rate constants; Reaction kinetics; Respiration; Stopped‐flow spectroscopy; Synechocystis; Synechocystis PCC 6803; Stopped-flow spectroscopy; Plastocyanin; Cu; Cyanobacterium; PCC 6803; domain; Cytochrome oxidase; Electron transfer; Respiration; Characterization; Enzyme; Cyanobacteria; Cytochrome-c oxidase; Bacteria; Synechocystis; Oxidoreductases; Kinetics; Mass spectrometry
• ISSN: 0378-1097; 1574-6968
• DOI: 10.1016/j.femsle.2004.09.003

Abstract It has been shown that efficient functioning of photosynthesis and respiration in the cyanobacterium Synechocystis PCC 6803 requires the presence of either cytochrome c6 or plastocyanin. In order to check whether the blue copper protein plastocyanin can act as electron donor to cytochrome c oxidase, we investigated the intermolecular electron transfer kinetics between plastocyanin and the soluble CuA domain (i.e. the donor binding and electron entry site) of subunit II of the aa3-type cytochrome c oxidase from Synechocystis. Both copper proteins were expressed heterologously in Escherichia coli. The forward and the reverse electron transfer reactions were studied yielding apparent bimolecular rate constants of (5.1 ± 0.2) × 104 M−1 s−1 and (8.5 ± 0.4) × 105 M−1 s−1, respectively (20 mM phosphate buffer, pH 7). This corresponds to an apparent equilibrium constant of 0.06 in the physiological direction (reduction of CuA), which is similar to Keq values calculated for the reaction between c-type cytochromes and the soluble fragments of other CuA domains. The potential physiological role of plastocyanin in cyanobacterial respiration is discussed.