Steady-state kinetics of NADH:coenzyme Q oxidoreductase isolated from bovine heart mitochondria

Steady-state kinetics of the bovine heart NADH:coenzyme Q oxidoreductase reaction were analyzed in the presence of various concentrations of NADH and coenzyme Q with one isoprenoid unit (Q(1)). Product inhibitions by NAD(+) and reduced coenzyme Q(1) were also determined. These results show an ordered sequential mechanism in which the order of substrate binding and product release is Q(1)-NADH-NAD(+)-Q(1)H(2). It has been widely accepted that the NADH binding site is likely to be on the top of a large extramembrane portion protruding to the matrix space while the Q(1) binding site is near the transmembrane moiety. The rigorous controls for substrate binding and product release are indicative of a strong, long range interaction between NADH and Q(1) binding sites.