108] Cephalopod retinochrome

Abstract

Publisher Summary This chapter discusses the cephalopod retinochrome. The cephalopod retina has a dual system of photosensitive chromoproteins with retinaldehyde as chromophores rhodopsin and retino-chrome. Rhodopsin is associated only with microvillar membranes of the outer segments of visual cells, whereas retinochrome is found in both inner and outer segments. The two photopigments differ from each other in the stereoisomeric form of their chromophore retinal, which is 11- cis in rhodopsin but all- trans in retinochrome. Retinochrome can be extracted also from the released fragments of outer segments. In the squid Loligo pealei , it is contained equally in both the inner and outer segments, and in Todarodes pacificus, much more is found in the outer segments. As retinochrome in the outer segments increases markedly during light adaptation of animal, it seems likely that some retinochrome protein moves forward from the inner to the outer segments and reacts there with metarhodopsin.