Biosynthesis
Retinoic acid can be produced in the body by two sequential oxidation steps that convert retinol to retinaldehyde to retinoic acid, but once produced it cannot be reduced again to retinol. The enzymes that generate retinoic acid for control of gene expression include retinol dehydrogenases (i.e. Rdh10) that metabolize retinol to retinaldehyde, and retinaldehyde dehydrogenases: RALHD1 (ALHD1A1), RALHD2 (ALHD1A2), and RALHD3 (ALHD1A3) that metabolize retinaldehyde to retinoic acid. Enzymes that metabolize excess retinol to prevent toxicity include alcohol dehydrogenase and cytochrome P450(cyp26).
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