Formation and storage of 11-cisretinol in the eyes of lobster (Homarus) and crayfish (Procambarus)

Abstract

AbstractModes of storage and mechanisms of formation of 11-cisretinoids in the eyes of animals vary widely among the major phyla. We here describe evidence from two species of macruran decapod crustacea that point to different processes from those known in insects, the other group of arthropods for which there is extensive data. The eyes of the lobster (Homarus) contain about 300 pmol of retinal, somewhat less free retinol, and variable amounts (up to 1000+ pmol) of two retinyl esters, over 90% of which contain retinol in the 11-cisconfiguration. The major ester contains the long chain, polyunsaturated fatty acid docosahexaenoate (C22:6), but retinyl oleate (C18:1) is also present. Crayfish (Procambarus) contain the same retinyl esters, although in much smaller amounts. Homogenates of the eyes of both species are capable of isomerizing all-transretinyl docosahexaenoate to the 11-cisconfiguration without using the energy of light. Crude fractionation of homogenates shows isomerase activity associated with membranes. The reaction mechanism has not been explored in detail, but on the basis of present evidence it may be similar to that found in vertebrate pigment epithelium. It is clearly different from the light-dependent processes known in insects (HymenopteraandDiptera) and cephalopod mollusks, where isomerization takes place at the level of the aldehyde and 11-cisretinyl esters are not present as major storage reserves.