Redox internal electron transfer kinetics

M. Fabian and co-workers have studied the protein s role in internal electron transfer to the catalytic center of cytochrome c oxidase using stopped-flow kinetics. Mitochondrial cytochrome c oxidase, CcO, an enzyme that catalyzes the oxidation of ferrocytochrome c by dioxygen, is discussed more fully in Section 7.8. In the overall process, O2 is reduced to water, requiring the addition of four electrons and four protons to the enzyme s catalytic center. Electrons enter CcO from the cytosolic side, while protons enter from the matrix side of the inner mitochondrial membrane. This redox reaction. 

Xanthine Oxidase. This molybdoenzyme is readily available from cows milk in gram quantities (28) and is relatively stable, which accounts for the fact that it is by far the most intensively studied molybdoenzyme. Bray and Swann (5) have reviewed comprehensively the earlier literature, and recent papers by Olson et al. (20) summarize combined kinetic and thermodynamic approaches to the states of the prosthetic groups during catalysis. Two molybdenum, four iron-sulfur centers, and two FAD groups are present in each molecule. An important point raised by Edmondson, et al. (29) is that the rates of internal electron transfer among the prosthetic groups appear to be much more rapid than turnover. Olson et al., (20) deduced that the reduction potentials of the two processes Mo(VI) <— Mo(V) <— Mo(IV) were —60 and —31 mv, respectively, relative to the redox potential for one of the iron-sulfur centers (center II) in the molecule. Thus, at equilibrium one can never have more than a small fraction of molybdenum as... 

The rate behaviour for the reduction of salicylato and several substituted salicylato derivatives of [(NH3)5Co] was consistent with the intervention of chelated precursor complexes formed from the two cobalt(iii) centres with loss of H, after which internal electron-transfer competes with non-productive dissociation of the precursor. The kinetics of reduction by chromium(ii) of a series of 2-hydroxy-benzenato derivatives of [(NH3)5Co] were compared with those of the 2-amino-benzoate derivatives. A study of the kinetics of dissociation of oxalatobis(phenan-throline)cobalt(iii) into cis-d iaquobis(phenanthroline)cobalt(iii) in aqueous HCl-KCl media found the rate was first order with respect to The photo-redox... 

The investigation of the kinetics and mechanisms of electron transfer reactions between metalloproteins and with inorganic redox reactants continues to be a rapidly growing field. The Proceedings of the 3rd International Conference on Bioinorganic Chemistry (1987) have been published in a special issue of Recueil des Travaux Chimiques des Pay-Bas, and include a section on metalloprotein electron transfer. The subject of long-distance electron transfer in metalloproteins has also been reviewed. 

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