Filling the gap in vitamin A research - Molecular identification of an enzyme cleaving beta-carotene to retinal

Vitamin A and its derivatives (retinoids) are essential components in visio n; they contribute to pattern formation during development and exert multip le effects on cell differentiation with important clinical implications. It has been known for 50 years that the key step in the formation of vitamin A is the oxidative cleavage of beta-carotene; however, this enzymatic step has resisted molecular analysis. A novel approach enabled us to clone and i dentify a beta-carotene dioxygenase from Drosophila melanogaster, expressin g it into the background of a beta-carotene (provitamin A)-synthesizing and -accumulating Escherichia coli strain. The carotene-cleaving enzyme, ident ified here for the first time on the molecular level, is the basis of the n umerous branches of vitamin A action and links plant and animal carotene me tabolism.