Characteristics of rotenone-insensitive oxidation of matrix-NADH by broad bean mitochondria.

Mitochondria from Vicia faba L. exhibit two pathways for the oxidation of endogenous NADH. One pathway is rotenone-sensitive and includes three phosphorylation sites, the other one is rotenone-insensitive and by-passes site I. This by-pass is located in the area of flavoproteins, but several lines of evidence suggest that the rotenone-insensitive oxidation of matrix-NADH is not mediated by the external NADH dehydrogenase. With saturating substrate concentrations the two pathways are superimposed in state 3 while in state 4 the electrons are transferred only via the by-pass. The rotenone-resistant electron flux is obviously regulated from the substrate side. We suggest that the function of the by-pass is to regulate the NADH/NAD(+) ratio of the matrix space.