Kinetic distinction between cytochromes a and a3 in cytochrome c oxidase. Rapid scanning stopped flow study of anaerobic reduction by a neutral and a negatively charged donor.
1981; Elsevier BV; Volume: 256; Issue: 3 Linguagem: Inglês
10.1016/s0021-9258(19)69926-6
ISSN1083-351X
AutoresFolim G. Halaka, Ǵerald Babcock, James L. Dye,
Tópico(s)Microbial Fuel Cells and Bioremediation
ResumoAnaerobic reduction of cytochrome c oxidase by 5,lOdihydro-5-methylphenazine (reduced PMS) and by sodium dithionite were studied by rapid scanning stopped flow spectrophotometry.In both cases the decay of the Soret band of the oxidized oxidase is not uniform.With reduced PMS, the reduction involves two molecules of reductant (4 electrons)/oxidase molecule.The first stage of the reduction exhibits an isosbestic point in the Soret region at 437 nm.This shifts to 428 nm in later stages of the reaction.The reduction of the oxidase by sodium dithionite is also complete and apparently involves SO:.In this case the spectra show an isosbestic point at -420 n m which shifts to 432 nm as the reaction proceeds.For each of the reductants the reaction is best described by three phases: the first is a second order reaction between the oxidase and the reductant, followed by two first order processes which appear to describe the intramolecular electron redistribution within the oxidase molecule.The results agree with the assignment of the Soret band of the oxidase molecule to cytochrome as with an absorption maximum near 410 nm and to cytochrome a which has its maximum absorption near 430 nm.If these assignments are correct, the present data show that reduced PMS, an uncharged molecule, reacts more rapidly with cytochrome a than it does with cytochrome as, while the negatively charged radical anion, SO:, appears to have more direct access to cytochrome U S .Cytochrome c oxidase (EC 1.9.3.1) is the terminal oxidase in the mitochondrial electron transport chain and catalyzes the reduction of molecular oxygen to water (Lemberg, 1969; Malmstrom, 1979).The activity of the protein is due to its two iron centers, present as cytochromes a and ai, and two copper ions.Studies of the reduction kinetics of the oxidase have been done using mainly fixed wavelength stopped flow absorption techniques (Gibson et al.,
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