The enzymatic cleavage of beta-carotene into vitamin A by soluble enzymes of rat liver and intestine.

Abstract

Radio [beta]-carotene suspended in a micellar solution in Tween 40 is converted to retinal and retinol by a high-speed supernatant solution of rat liver and intestine. The 1st product of the reaction seems to be retinal, which was characterized by reduction to retinol and then dehydration to anhydro-retinol. [beta]-Apo-carotenols and carotenals were not detected in the incubation solution. The enzyme is inhibited by sulfhydryl binding agents, protected by cysteine, and inhibited after preincubation with [alpha],[alpha][image]-dipyridyl, ortho-phenanthroline, and ethylenediaminetetraacetate. Cyanide did not inhibit appreciably at concentrations which completely inactivate ferric protoporphyrin enzymes. Oxygen is required for the reaction. Bile salts, although essential for the uptake and cleavage of [beta]-carotene into retinyl ester by intestinal slices in vivo and in vitro, are not required for the cleavage reaction in intestinal homogenates. In view of the properties of the enzyme, it has tentatively been termed [beta]-carotene 15-15[image] oxygenase.