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 endoplasmic reticulum vesicles capable of forming 50-60 nm buds in the presence of ATP and retinol was assayed for retinol-responsive oxidation of NADH and cleavage of a dithiodipyridine (DTDP) protein disulfide-thiol interchange substrate. Maxima for the two activities alternated giving rise to a 24 min period. The NADH oxidase activity was inhibited by micromolar and submicromolar concentrations of retinol. Retinol at 0.1 mM stimulated the activity. The inhibition was confined to two activity maxima separated in time by about 5 min. In contrast, with the DTDP substrate, the activity was stimulated by retinol and the stimulations were in the part of the oscillatory pattern where retinol inhibition of NADH oxidation was observed. The findings support an earlier proposed mechanism whereby retinol exerted opposing effects on NADH oxidation and protein disulfide reductions.