Periodic NADH oxidase activity associated with an endoplasmic reticulum fraction from pig liver. Response to micromolar concentrations of retinol

An endoplasmic reticulum fraction from pig liver enriched in transitional e ndoplasmic reticulum vesicles capable of forming 50-60 nm buds in the prese nce of ATP and retinol was assayed for retinol-responsive oxidation of NADH and cleavage of a dithiodipyridine (DTDP) protein disulfide-thiol intercha nge substrate. Maxims for the two activities alternated giving rise to a 24 min period. The NADH oxidase activity was inhibited by micromolar and subm icromolar concentrations of retinol. Retinol at 0.1 mM stimulated the activ ity. The inhibition was confined to two activity maxima separated in time b y about 5 min. In contrast, with the DTDP substrate, the activity was stimu lated by retinol and the stimulations were in the part of the oscillatory p attern where retinol inhibition of NADH oxidation was observed. The finding s support an earlier proposed mechanism whereby retinol exerted opposing ef fects on NADH oxidation and protein disulfide reductions. (C) 2000 Elsevier Science B.V. All rights reserved.