Studies on the respiratory chain-linked reduced nicotinamide adenine dinucleotide dehydrogenase. XI. Transformation of the dehydrogenase to reduced nicotinamide adenine dinucleotide-coenzyme Q reductase.

Purified preparations of the reduced nicotinamide adenine dinucleotide dehydrogenase of the respiratory chain, extracted with the aid of phospholipase at moderate temperature, do not catalyze the reduction of long chain coenzyme Q derivatives (Q6 and QIO) at significant rates and are not inhibited by amytal or rotenone. On exposure of the enzyme to conditions which have been used for the extraction of NADH-coenzyme Q reductase (pH 5.4, 9.5% ethanol 43” for 15 min) the characteristic properties and catalytic activities of the dehydrogenase are lost and a high catalytic activity toward coenzyme Q6 and Qlo emerges, along with cytochrome c reductase activity. The NADH-coenzyme Q reductase activity created by this treatment is comparable to that obtained on direct extraction of submitochondrial particles with acid-ethanol at 43” and is inhibited by amytal and rotenone to the same extent as NADH-coenzyme Q reductase. The lack of rotenoneand amytal-sensitive coenzyme Q reductase activity in NADH dehydrogenase is not due to the exposure of the preparation to pH 8.5 or to phospholipase A, as has been suggested by other authors, since submitochondrial particles isolated at pH 8.5 and at neutral pH are equally good sources of soluble NADHcoenzyme Q reductase and since neither cobra venom nor its constituent phospholipase A inhibit or inactivate soluble NADH-coenzyme Q reductase. The reason why venom treatment of particles interferes with subsequent extraction of NADH-coenzyme Q reductase by heat-acid-ethanol is that an inhibitor is formed by the venom, which can be removed, however, with the aid of serum albumin. Evidence