The enzymatic cleavage of beta-carotene: end of a controversy.

The central cleavage of dietary beta-carotene to retinal was found to be the predominant mechanism whereby retinoids were formed in vivo in rats; apo-carotenals, indicative of eccentric cleavage of beta-carotene, were only a minor component (<5% of retinoids). A gene from maize that codes for a plant carotenoid cleavage enzyme was used to isolate a homologous gene from Drosophila. This gene, when transfected into an E Coli strain capable of synthesizing and accumulating beta-carotene, caused the central cleavage of beta-carotene, forming exclusively retinoids. The enzyme that the gene codes for, beta-carotene-15,15'-dioxygenase, was purified and characterized.