Retinyl and 3-dehydroretinyl esters in the crayfish retina

We have studied chemical nature and localization of retinyl esters stored in the retina of the crayfish, Procambarus clarkii, which has a rhodopsin-porphyropsin visual pigment system. The crayfish kept at 10 degrees C in the constant dark had 3-dehydroretinal along with retinal in the retina as the chromophore of visual pigment. Both retinyl and 3-dehydroretinyl esters were found in the retina, more than 95% of them in the 11-cis configuration. Of three kinds of fatty acid detected in the esters, the major component (about 80%) was the polyunsaturated fatty acid, docosahexaenoic acid (C22 = 6). Observations with electron and fluorescence microscopy and the results of fractionation experiments showed that the esters were stored in photoreceptor cells as oil droplets. The ratio of 3-dehydroretinal/retinal as visual pigment chromophore was always higher than that of 3-dehydroretinol/retinol in the stored esters. This result suggests a mechanism of selective utilization of 3-dehydroretinol for the chromophore of visual pigment in the crayfish retina.