Journal of Lipid Research, Vol. 5, 281-299, July 1964
Copyright © 1964 by Lipid Research, Inc.

The biosynthesis and metabolism of carotenoids and retinol (vitamin A)

James Allen Olson

Department of Biochemistry, University of Florida College of Medicine, Gainesville, Florida

Acetate, by condensation and decarboxylation reactions, is converted to isopentenyl pyrophosphate, which condenses to form C₂₀ terpenol pyrophosphates. These latter compounds condense to yield the initial C₄₀ carotenoid precursor which is presumably phytoene. By a series of dehydrogenation, cyclization, isomerization, and hydration reactions, various acyclic and alicyclic carotenoids are formed. Subsequently, hydroxylation, epoxidation, and oxidation-reduction reactions may occur. Several carotenoids and ßbeta;-apocarotenals may be converted into retinol in mammalian tissues. Thereafter, retinol may be esterified, oxidized to retinal and retinoic acid, isomerized, and further metabolized. This review has stressed the route by which these transformations occur and the characteristics of the enzymes involved rather than nutritional, functional, or chemical aspects of carotenoids.

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