 All-trans-retinyl ester

An all-trans-retinyl ester is a retinyl ester whose retinyl-chain double bonds have trans geometry. The prefix specifies that part of the molecule; the attached acyl group can still vary. A sample described only by this class name is consequently not a completely specified individual compound.^[ref]

Two independent structural choices are involved. Changing the attached acyl group can alter the molecular formula while leaving retinyl-chain geometry unchanged. Changing one retinyl double bond from trans to cis instead changes the geometry without necessarily changing the molecular formula. Esterification and cis-trans isomerism must therefore be distinguished.

The distinction has a concrete role in the visual cycle. A 2005 expression experiment showed that RPE65 converts an all-trans-retinyl ester substrate into 11-cis-retinol, provided the cells also expressed the substrate-supplying lecithin retinol acyltransferase.^[ref] The observed product differs in both ester status and retinyl geometry. Measuring only total retinoid would conceal those chemically important changes.