= 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.<All-trans-retinyl ester in ChEBI>[CHEBI:63410, Definition and generic structure]{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>.<RPE65 is the isomerohydrolase in the retinoid visual cycle by Gennadiy Moiseyev and others>[Abstract, supplied ester substrate and 11-cis product]{ref} The observed product differs in both ester status and retinyl geometry. Measuring only total <retinoid> would conceal those chemically important changes.
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