Characterization of a novel g' = 2.95 EPR signal from the binuclear center of mitochondrial cytochrome c oxidase.
The oxidized binuclear heme a3/CuB center of slow forms of bovine cytochrome oxidase exhibits a characteristic EPR signal at g' = 12. Following the (rapid) dithionite reduction of heme a and CuA, an additional EPR signal becomes apparent at g' = 2.95. As electrons enter the binuclear center this signal decays at the same slow rate as the g' = 12 signal. In the fully oxidized slow enzyme the small g' = 2.95 signal is usually masked by the g = 3 heme a signal, but it is readily detectable at low temperatures and high microwave powers. It is present in both the intrinsic and formate-ligated slow enzymes, but not in any form of fast preparation. The g' = 2.95 signal has similar temperature dependence and microwave power saturation characteristics to the g' = 12 signal. We conclude that the signal arises from the same population of binuclear centers responsible for the g' = 12 signal. The appearance of a signal at g' = 2.95 in X-band EPR is consistent with, but does not prove, the model of Hagen where the g' = 12 signal arises from a ferryl heme a3, with CuB cuprous and EPR-silent (Hagen, W. R. (1982) Biochim. Biophys. Acta 708, 82-98).
Cooper
C E
CE
Division of Biomolecular Sciences, King's College London, United Kingdom.
Salerno
J C
JC
D000818:Animals; D002417:Cattle; D004227:Dithionite / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000378:metabolism* / Q000528:radiation effects; D006418:Heme / Q000031:analogs & derivatives / Q000378:metabolism; D008872:Microwaves; D008929:Mitochondria, Heart / Q000201:enzymology; D013696:Temperature
D004227:Dithionite; C027728:heme a; D006418:Heme; D003576:Electron Transport Complex IV