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Definition of Vitamin a1
1. Noun. An unsaturated alcohol that occurs in marine fish-liver oils and is synthesized biologically from carotene.
Medical Definition of Vitamin a1
1. Vitamin A1alcohol; 2,6,6-trimethyl-1-(9'-hydroxy-3',7'-dimethylnona-1',3',5',7'-tetraenyl)cyclohex-1-ene;a half-carotene bearing the b (or beta-ionone) form of the cyclic end group and a CH2OH at the C-15 position (numbering as in carotenoids) or 9'-position (numbering as a nonyl side chain on a cyclohexene ring); an intermediate in the vision cycle, it also plays a role in growth and differentiation. See: dehydroretinol. Synonym: vitamin A1 alcohol, vitamin A1. Retinol dehydrogenase, an oxidoreductase catalyzing interconversion of retinal and NADH to retinol and NAD+. (05 Mar 2000)