Oxidation of cytosolic NADH via complex I of heart mitochondria.

The exogenous NADH dehydrogenase of heart mitochondria is increasingly reported to mediate cardiomyopathies following adriamycin treatment or reperfusion of ischemic hearts. A great number of studies on the biochemistry and pathobiology exists which indirectly support the existence of this dehydrogenase. Our studies exclude both the rotenone-insensitive NADH dehydrogenase of the outer membrane and the endogenous NADH dehydrogenase of damaged mitochondria as being responsible for external NADH consumption. Reducing equivalents from external NADH were demonstrated to enter complex I of the respiratory chain from the cytosolic phase. Our data support earlier reports on the physical association of the exogenous NADH dehydrogenase with the inner mitochondrial membrane excluding oxidation of external NADH via an enzyme of artefactual origin.