Effect of the side chain structure of coenzyme Q on the steady state kinetics of bovine heart NADH:coenzyme Q oxidoreductase

Steady state kinetics of bovine heart NADH: coenzyme Q oxidoreductase using coenzyme Q with two isoprenoid unit (Q(2)) or with a decyl group (DQ) show an ordered sequential mechanism in which the order of substrate binding and product release is NADH-Q(2) (DQ)-Q(2)H(2) (DQH(2))-NAD(+) in contrast to the order determined using Q(1) (Q(1)-NADH-NAD(+)-Q(1)H(2)) (Nakashima et al., J. Bioenerg. Biomembr. 34, 11-19, 2002). The effect of the side chain structure of coenzyme Q suggests that NADH binding to the enzyme results in a conformational change, in the coenzyme Q binding site, which enables the site to accept coenzyme Q with a side chain significantly larger than one isoprenoid unit. The side chains of Q(2) and DQ bound to the enzyme induce a conformational change in the binding site to stabilize the substrate binding, while the side chain of Q(1) (one isoprenoid unit) is too short to induce the conformational change.