The enzyme converted these carotenoids to beta-apo-13-carotenones by cleaving their C_13-C_14 double bonds. The oxygen atom of beta-apo-13-carotenone originated not from water but from molecular oxygen. Thus, the enzyme was an apo-carotenoid 13,14-dioxygenase....
Initially, we explored the effects of beta-apo-13-carotenone and beta-apo-14'-carotenal on P19 cells, a mouse embryonal carcinoma cell line that differentiates into neurons when treated with all-trans-retinoic acid. Treatment of P19 cells with either compound failed to block all-trans-...