Proteins of Invertebrate Photoreceptor Membranes

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Abstract
Polyarcylamide‐gel electrophoresis on digitonin and dodecylsulphate gels has been used to characterize visual pigment preparations obtained from rhabdomeric photoreceptors. The rhodopsin of the cephalopod Eledone moschata (P470) and the ultraviolet‐sensitive visual pigment of the insect Ascalaphus macaronius (P345) were separated from non‐rhodopsin proteins by electrophoresis on digitonin gels. Visual pigment bands in the digitonin gel were located by their absorbances and photoreactions. The mobility of visual pigment protein on sodium dodecylsulphate‐polyacrylamide gels run in parallel with marker proteins indicated a polypeptide chain with a molecular weight of approximately 43 000 for P470 and 35 000 for P345. When digitonin extracts of P470 were stored before use, a decrease in the electrophoretic mobility of the dodecyl‐sulphate‐denatured pigment was observed, raising the apparent molecular weight to about 51 000. The data indicate that the protein components of vertebrate and invertebrate visual pigments are similar in size.