Feedback regulation of beta,beta-carotene 15,15'-monooxygenase by retinoic acid in rats and chickens.

beta,beta-Carotene 15,15'-monooxygenase (formerly termed beta,beta-carotene 15,15'-dioxygenase, EC 1.13.11.

The bioavailability of alpha- and beta-carotene is affected by gut microflora in the rat.

The present study examined whether the intestinal microflora could affect the bioavailability and vitamin A activity of dietary alpha- and beta-carotene in the rat. In the first set of experiments, we used conventional, germ-free (axenic), and human-flora-associated (heteroxenic) rats. In a second series, conventional rats were treated with either an antibiotic mixture or a potent inhibitor of gastric secretion (Omeprazole).

In vitro and in vivo inhibition of beta-carotene dioxygenase activity by canthaxanthin in rat intestine.

beta-Carotene dioxygenase catalyzes the conversion of provitamin A carotenoids to vitamin A in mammalian tissues. Whether the enzyme can also cleave non-provitamin A carotenoids to retinoid analogs with biological activities is still unclear. We investigated (i) substrate specificities of beta-carotene dioxygenase toward provitamin A and non-provitamin A carotenoids and (ii) potential antagonistic effects of non-provitamin A carotenoids on beta-carotene conversion to vitamin A.

Rat intestinal beta-carotene dioxygenase activity is located primarily in the cytosol of mature jejunal enterocytes.

The purposes of this study were to determine the location of beta-carotene dioxygenase (EC 1.13.11.