Kinetics of electron transfer between plastocyanin and the soluble CuA domain of cyanobacterial cytochrome c oxidase.
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) x 10(4) M(-1) s(-1) and (8.5+/-0.4) x 10(5) 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.
Department of Physical Chemistry, Molecular Bioenergetics Group, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
Martina
M
Paumann
Margit
M
Bernroitner
Borjana
B
Lubura
Michael
M
Peer
Christa
C
Jakopitsch
Paul G
PG
Furtmüller
Günter A
GA
Peschek
Christian
C
Obinger
D003300:Copper / Q000737:chemistry; D000458:Cyanobacteria / Q000201:enzymology*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry*; D004583:Electrons; D007700:Kinetics; D010970:Plastocyanin / Q000737:chemistry*
D003300:Copper; D010970:Plastocyanin; D003576:Electron Transport Complex IV