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- Title
Kinetics of interprotein electron transfer between cytochrome <f>c<sub>6</sub></f> and the soluble Cu<sub>A</sub> domain of cyanobacterial cytochrome <f>c</f> oxidase
- Authors
Paumann, Martina; Feichtinger, Markus; Bernroitner, Margit; Goldfuhs, Judith; Jakopitsch, Christa; Furtmüller, Paul G.; Regelsberger, Günther; Peschek, Günter A.; Obinger, Christian
- Abstract
Cytochrome <f>c6</f> is a soluble metalloprotein located in the periplasmic space and the thylakoid lumen of many cyanobacteria and is known to carry electrons from cytochrome <f>b6f</f> to photosystem I. The CuA domain of cytochrome <f>c</f> oxidase, the terminal enzyme which catalyzes the four-electron reduction of molecular oxygen in the respiratory chains of mitochondria and many bacteria, also has a periplasmic location. In order to test whether cytochrome <f>c6</f> could also function as a donor for cytochrome <f>c</f> oxidase, we investigated the kinetics of the electron transfer between recombinant cytochrome <f>c6</f> (produced in high yield in Escherichia coli by coexpressing the maturation proteins encoded by the ccmA-H gene cluster) and the recombinant soluble CuA domain (i.e., the donor binding and electron entry site) of subunit II of cytochrome <f>c</f> oxidase from Synechocystis PCC 6803. The forward and the reverse electron transfer reactions were studied by the stopped-flow technique and yielded apparent bimolecular rate constants of (3.3 ± 0.3) × 105 M-1 s-1 and (3.9 ± 0.1) × 106 M-1 s-1, respectively, in 5 mM potassium phosphate buffer, pH 7, containing 20 mM potassium chloride and 25 °C. This corresponds to an equilibrium constant <f>Keq</f> of 0.085 in the physiological direction (<f>ΔrG′0=6.1</f> kJ/mol). The reduction of the CuA fragment by cytochrome <f>c6</f> is almost independent on ionic strength, which is in contrast to the reaction of the CuA domain with horse heart cytochrome <f>c</f>, which decreases with increasing ionic strength. The findings are discussed with respect to the potential role of cytochrome <f>c6</f> as mobile electron carrier in both cyanobacterial electron transport pathways.
- Subjects
OXYGEN; PROTEINS; PHOSPHATES; CYTOCHROME oxidase
- Publication
FEBS Letters, 2004, Vol 576, Issue 1/2, p101
- ISSN
0014-5793
- Publication type
Article
- DOI
10.1016/j.febslet.2004.08.070