Metabolism and biologicalpotency of 5,-monoepoxy-beta-carotene and 5,6:5',6'-diepoxy-beta-carotene.

1. 5,6-Monoepoxy-beta-carotene and 5,6:5',6'-diepoxy-beta-carotene were partially converted into the furanoid forms during passage through the rat stomach. 2. The monoepoxide was converted into vitamin A in the small intestine and showed a biological potency 21% of that of beta-carotene. Neither beta-carotene nor 5,6-monoepoxyvitamin A was formed. 3. Intraperitoneal administration of the monoepoxide led to the accumulation of the unchanged compound in the liver and other tissues. 4. The diepoxide gave no beta-carotene or vitamin A or 5,6-monoepoxyvitamin A when given orally and showed no biological potency. 5. The significance of these results with special reference to the mechanism of formation of vitamin A from beta-carotene is discussed.