Kinetic control of internal electron transfer in cytochrome c oxidase

Article type: Research Article

Authors: Brunori, Maurizio^; | Giuffrè, Alessandro | D’Itri, Emilio | Sarti, Paolo

Affiliations: Department of Biochemical Sciences “A. Rossi‐Fanelli” and CNR Center of Molecular Biology, University of Rome “La Sapienza”, I‐00185 Rome, Italy

Note: [] To whom correspondence should be addressed: Dipartimento di Scienze Biochimiche “A. Rossi‐Fanelli”, Universita’ di Roma “La Sapienza”, Piazzale Aldo Moro 5, I‐00185 Roma, Italia. Tel.: 39 6 4450291; Fax: 39 6 4440062; E‐mail: [email protected].

Abstract: Two alternative hypotheses have been proposed to account for the relatively slow (ms) internal eT observed in the oxidized cyt c oxidase. The thermodynamic control hypothesis states that eT between cyt a and a_{3} is very fast (\mus), but the apparent reduction of cyt a_{3} is slow because thermodynamics favors reduced cyt a. Whereas the kinetic control hypothesis states that inter‐heme eT is intrinsically slow (ms), for the oxidized binuclear center. Monitoring by stopped flow the anaerobic reduction of the oxidized enzyme by ruthenium hexamine in the absence and presence of CO or NO, used as “trapping” ligands for cyt a_{3}^{2+}, we found that the rate of formation of the cyt a_{3}^{2+}–NO adduct (k' \approx 20–25 s^{-1}) is independent of the concentration of ruthenium hexamine and NO. We conclude that in the oxidized enzyme the two hemes are not in very rapid redox equilibrium and internal eT is kinetically controlled.

Journal: Biofactors, vol. 8, no. 3-4, pp. 191-193, 1998