RAT INTESTINAL BETA-CAROTENE DIOXYGENASE ACTIVITY IS LOCATED PRIMARILY IN THE CYTOSOL OF MATURE JEJUNAL ENTEROCYTES

location of beta-carotene dioxygenase (EC 1.13.11.21) activity within the rat gastrointestinal tract, within the villus and within enterocyt es, and to identify the metabolites produced in each intestinal fracti on. In Wistar female rats, maximal activity was detected in the cytoso l (74-93% of the total cellular activity) of mature functional enteroc ytes harvested from the jejunum (67% of the intestinal activity). The specific activity, expressed in pmol of retinoids/ (h . mg protein) ro se from 49 +/- 3 in the stem cells to 199 +/- 12 in the mature functio nal cells (P < 0.05). Thus the intestinal beta-carotene cleavage activ ity might be regulated during the enterocyte maturation process. By us ing HPLC with diode array and radioactive detectors, retinal, and in t he presence of NAD(+), retinoic acid, were identified as the only meta bolites produced. No beta-12'-, 10'-, and 8'-apo-carotenals were detec ted, even when various enzyme sources were tested. These results sugge st that the major, if not the sole, pathway for the formation of vitam in A from beta-carotene in the rat intestine is central cleavage.