Purification and properties of carotene 15,15′-dioxygenase of rabbit intestine
1972
M.R. Lakshmanan | Hansa Chansang | James A. Olson
Carotene 15,15′-dioxygenase, which oxidizes carotenoids to retinal, has been purified up to 200-fold from rabbit intestine by ammonium sulfate fractionation, heat treatment, and acetone precipitation. With β-apo-10′-carotenol as the substrate, the purified enzyme has a pH optimum of 7.8, a Km, of 6.7 × 10–5 m, and a Vmax at 37°C of 9 nmoles of retinal/mg protein/hr. The purified enzyme is inhibited by ferrous ion-chelating agents such as α,α′-dipyridyl and o-phenanthroline, and by sulfhydryl-binding agents such as iodoacetamide, N-ethylmaleimide, and p-chloromercuribenzoate. The latter inhibitory effects are reversed by reduced glutathione. The cleavage of β-apo-10′-carotenol is competitively inhibited by its acetylenic analog, 15,15′-dehydro-β-apo-10′-carotenol. The enzyme is present in the intestinal mucosa of several mammals, the chicken, the tortoise, and a freshwater fish, but it is absent from cat intestinal tissue.
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