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 (Q1). Product inhibitions by NAD+ and reduced coenzyme Q1 were also determined. These results show an ordered sequential mechanism in which the order of substrate binding and product release is Q1-NADH-NAD+-Q1H2. 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 Q1 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 Q1 binding sites.