Human cytochrome P450 27C1 catalyzes 3,4‐desaturation of retinoids

In humans, a considerable fraction of the retinoid pool in skin is derived from vitamin A2 (all‐trans 3,4‐dehydroretinal). Vitamin A2 may be locally generated by keratinocytes, which can convert vitamin A1 (all‐trans retinol) into vitamin A2 in cell culture. We report that human cytochrome P450 (hP450) 27C1, a previously ‘orphan’ enzyme, can catalyze this reaction. Purified recombinant hP450 27C1 bound and desaturated all‐trans retinol, retinal, and retinoic acid, as well as 11‐cis‐retinal. Although the physiological role of 3,4‐dehydroretinoids in humans is unclear, we have identified hP450 27C1 as an enzyme capable of efficiently mediating their formation.