Question

why is it important for the function of the mitochondrial electron transport chain for the value of E of cytochrome c to fall between 0.22 and 0.29V

Answer 1

A successful catalyst must display a low activation potential for NADH oxidation, high catalytic activity, and high stability. For most catalysts above, activation is controlled by the redox potential of the catalyst, which should ideally be as close to the formal potential of NADH as possible. Stability of quinones, pyrroles, and other materials may be enhanced by electropolymerization of the catalyst onto an electrode surface.For some species, such as azines, electropolymerization results in a positive shift in redox potential, and therefore potential of NADH activation. For example, the redox potential of toluidene blue-o (TBO) increases from −0.11 V/SHE to 0.22V/SHE (0.29–0.62V/RHE, pH 6.7) upon polymerization. Such a shift can enhance the kinetics of NADH oxidation at the expense of higher anode operating potential. Electropolymerization tends not to affect the redox potential of quinones. The enzyme diaphorase (NAD(P)H dehydrogenase, EC, in conjunction with an additional mediator has been shown to provide very high NADH oxidation rates. Diaphorase, a membrane (extrinsic) flavoprotein containing iron–sulfur electron transfer clusters, is a natural electron acceptor from NADH as part of the mitochondrial electron transport chain.