Vitamin A2
Vitamin A2 is a subcategory of vitamin A.
As with all vitamin A forms, A2 can exist as an aldehyde, Dehydroretinal, an alcohol, 3,4-dehydroretinol or an acid, 3,4-dehydroretinoic acid. Many cold-blooded vertebrates use the aldehyde for their visual system to obtain a red-shifted sensitive spectrum.
Human skin naturally contains the alcohol form. In humans, CYP27C1 converts ordinary A1 to A2. The enzyme also converts 11-cis-retinal.
Vitamin A2 was first identified by Richard Alan Morton using newly-developed absorption spectroscopy in 1941.