Evidence for a two proton dependent redox equilibrium in an archaeal Rieske iron-sulfur cluster.
The recently detected Rieske iron-sulfur center in the membrane of the thermoacidophilic archaeon Sulfolobus acidocaldarius (Anemüller et al., 1993, FEBS Lett. 318, 61-64) was further characterized by EPR spectroscopy, coupled to redox-potentiometry and functional studies. The reduction potential is pH-dependent above pH 6, revealing the influence of two ionization equilibria in the oxidized form, with pKaox-values of 6.2 and 8.5. Above pH 9, the slope of the curve is--120 mV/pH-unit. A partially purified fraction exerted a ubiquinol-cytochrome c oxidoreductase activity. To our knowledge, for the first time, in a membrane bound Rieske iron-sulfur protein, unequivocal evidence for a two proton dependent redox equilibrium is presented.
Anemüller
S
S
Instituto de Tecnologia Quimica e Biologica, Universidade Nova de Lisboa, Oeiras, Portugal.
Schmidt
C L
CL
Schäfer
G
G
Bill
E
E
Trautwein
A X
AX
Teixeira
M
M
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D014450:Electron Transport Complex III; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D010084:Oxidation-Reduction; D016945:Sulfolobus acidocaldarius / Q000378:metabolism*; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000494:pharmacology
D003574:Cytochrome c Group; D007506:Iron-Sulfur Proteins; D008565:Membrane Proteins; C037989:Rieske iron-sulfur protein; D014451:Ubiquinone; C060262:2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone; D014450:Electron Transport Complex III; D001205:Ascorbic Acid