Co-ordinated induction of beta-carotene cleavage enzyme and retinal reductase in the duodenum of the developing chicks

The developmental patterns of expression of beta -carotene cleavage enzyme activity were compared with those of retinal reductase and NAD-dependent re tinol dehydrogenase activities in chick duodenum during the perinatal perio d. The beta -carotene cleavage enzyme activity was not detected in the duod enum before hatching, but it increased rapidly during 24 h after hatching. On the other hand, a considerable level of beta -carotene cleavage enzyme a ctivity was observed in the liver of embryonic stages and its activity grad ually rose during the perinatal period. Comparison of kinetic constants for the beta -carotene cleavage enzyme activities in the duodenum and the live r indicated that the enzyme in the duodenum possessed a lower affinity for beta -carotene than that in the liver. The retinal reductase activity was d etected in the microsomes of the duodenum at the earliest time examined, i. e. day 16 of embryogenesis and its activity began to rise on the last day o f embryogenesis, which was followed by a gradual increase until 1 day of ag e. The NAD-dependent retinol dehydrogenase activity was also seen in the mi crosomes of the duodenum in embryonic stages and its activity increased in parallel with the retinal reductase activity around the hatching period. Th ese developmental inductions of beta -carotene cleavage enzyme and retinal reductase activities in the duodenum coincided with those of cellular retin ol-binding protein, type II (CRBPII) and lecithin: retinol acyltransferase (LRAT). These results suggest that a co-ordinated induction mechanism shoul d be operative for beta -carotene cleavage enzyme and retinal reductase, bo th of which are inevitable in the process of beta -carotene absorption and metabolism. (C) 2001 Elsevier Science Inc. All rights reserved.