16] Assay for carotenoid 15,15′-dioxygenase in homogenates of rat intestinal mucosal scrapings and application to normal and vitamin A-deficient rats

Abstract

β -Carotenoid 15,15'-dioxygenase, an oxygenase that cleaves β -carotene and certain related carotenoids, is the only known enzyme to be responsible for the formation of vitamin A (retinol) in vertebrates. It is of central importance in vitamin A nutrition for humans and for those animals that depend wholly or largely on plant foods. Its presence in the intestinal mucosa is consistent with its role in converting dietary carotenoids to vitamin A in vivo . Some studies have indicated that variations in dietary protein levels can affect the activity of the intestinal enzyme in rats, resulting in a reduced rate of conversion of β -carotene to vitamin A in protein-deficient animals. Dietary carotenoids may possibly increase the activity of the enzyme when dietary protein is limiting, and studies in laboratory have indicated that the enzyme can be induced by a dietary deficiency of vitamin A in rats.