Interphotoreceptor retinoid-binding protein and alpha-tocopherol preserve the isomeric and oxidation state of retinol

Retinol decomposes rapidly into a number of products, including its aldehyde form, retinal, when introduced into buffer in phospholipid vesicles or ethanol. Interphotoreceptor retinoid-binding protein at low concentrations is found to protect retinol from isomerization and oxidation. The addition of alpha-tocopherol to either liposomes or an ethanolic-buffer solution also prevents decomposition. Neither of these agents interferes with the successful regeneration of pigment with 9-cis retinal in rod outer segment preparations or the restoration of sensitivity by retinoids in isolated rod photoreceptors.