bims-resufa Biomed news
on Respiratory supercomplex factors
Issue of 2019‒03‒24
one paper selected by
Vera Strogolova
Marquette University

  1. Biochemistry. 2019 Mar 20.
    Blomberg MRA.
      Cytochrome c oxidase (C cO) is the terminal enzyme in the respiratory electron transport chain, reducing molecular oxygen to water. The binuclear active site in C cO comprise a high-spin heme associated with a CuB complex and a redox-active tyrosine. The electron transport in the respiratory chain is driven by increasing midpoint potentials of the involved cofactors, resulting in release of free energy, which is stored by coupling the electron transfer to proton translocation across a membrane, building up an electrochemical gradient. In this context, the midpoint potentials of the active site cofactors in the C cOs are of special interest, since they determine the driving forces for the individual oxygen reduction steps, and thereby affect the efficiency of the proton pumping. It has turned out to be difficult to obtain useful information on some of these midpoint potentials from experiment. However, since each of the reduction steps in the catalytic cycle of oxygen reduction to water corresponds to the formation of an O-H bond, they can be calculated with reasonably high accuracy using quantum chemical methods. From the calculated O-H bond strengths the proton coupled midpoint potentials of the active site cofactors can be estimated. Using models representing the different families of C cO's (A, B and C), the calculations give midpoint potentials that should be relevant during catalytic turnover. The calculations also suggest possible explanations for why some experimentally measured potentials deviate significantly from the calculated ones, i.e. for CuB in all oxidase families, and for heme b3 in the C-family.