Enzymatic oxidation of vitamin A aldehyde to vitamin A acid.

Studies indicating that vitamin A (1) and vitamin A aldehyde (2) are metabolized to water-soluble degradation products and CO% provide support for the suggestion (3) that there exists an oxidative pathway of major importance in the metabolism of vitamin A. The detection of vitamin A aldehyde in the liver (4, 5) and observations (6-8) that dietary vitamin A acid supports the growth of vitamin A-deficient animals are in accord with the view (3) that these compounds may be early intermediates in the proposed oxidative pathway. Recently, the oxidation of vitamin A aldehyde by aldehyde oxidase was described, and evidence was obtained for the formation of vitamin A acid from vitamin A aldehyde in the jejunum of the rat (9). However, other attempts to detect vitamin A acid as a metabolite of vitamin A have not been successful (10). Therefore, it was of interest that dialyzed liver extracts consumed vitamin A aldehyde, and that added diphosphopyridine nucleotide was stimulatory. Aldehyde-oxidizing enzymes were found to be involved in the disappearance of the aldehyde. This report describes the oxidation of Vitamin A aldehyde to vitamin A acid by liver aldehyde dehydrogenase, liver aldehyde oxidase, and milk xanthine oxidase.