MiP2005: Session 5

Mitochondrial Physiology Network 10.9: 61-62 (2005) - download pdf

 

Importance of primary reactions in cytochrome c oxidase for mitochondrial physiology.

Michael I Verkhovsky

Institute of Biotechnology, University of Helsinki, PB 65 (Viikinkaari 1), FIN-00014, Helsinki, Finland. - michael.verkhovsky@helsinki.fi

    Cytochrome c oxidase is a molecular energy transduction device. It catalyzes the reduction of dioxygen to water, and conserves the released energy into an electrochemical proton gradient (DmH+) that subsequently drives the synthesis of ATP. The enzyme requires four electrons and four protons to convert O2 into water. These electrons and protons are transferred into the O2 reduction site from opposite sides of the membrane, generating DmH+. In addition, for each O2 molecule reduced, the enzyme translocates four protons across the membrane, a process that doubles the efficiency of DmH+ formation.

    Cytochrome c oxidase evolved as an efficient energy conserving molecular machine, and as a result of this it cannot spend redox energy on oxygen binding. The dissociation constant of oxygen from the binuclear site of cytochrome c oxidase is on the order of 1 mM. At the same time apparent oxygen affinity measured as Km for oxygen is below 1 µM [1]. The presentation shows how molecular design can solve such a discrepancy. The second point of the presentation is to show by analyses of primary electron transfer events why the enzyme “professionally’ reducing oxygen never generates oxygen reactive species [2].

1.  Verkhovsky MI, Morgan JE, Puustinen A, Wikström M (1996) Kinetic trapping in cell respiration. Nature 380: 268-270.

2.  Morgan JE, Verkhovsky MI, Palmer G, Wikström M (2001). The role of the PR intermediate in the reaction of cytochrome c oxidase with O2.  Biochemistry 40: 6882-6892.

 


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