Visual pigments invertebrate

Visual excitation (1) in both vertebrates and invertebrates is initiated via light absorption by visual pigments consisting of a chromophore covalently bound to an apo-protein, opsin. Biochemical extraction studies have shown that in all pigments the chromophore is a Schiff base derivative of 11-cis retinal (Fig. 

In contrast, photoisomerization as a means for visual pigment regeneration appears to be the rule in invertebrates (Schwemer ra/., 1971 Haraera/., 1981). 

The native chromophore of vertebrate pigments is retinal and/or 3,4 dehydroretinal (found in certain aquatic species). In the invertebrate pigments, 3-hydroxyretinal [3,4] and 4-hydroxy-retinal [5] have also been found as the chromophore of visual pigments (Fig. 1). There has recently been an excellent review of the invertebrate pigments [6]. The discussion in this review will focus on the vertebrate systems. 

Gardner W, Towner P (1995) Invertebrate visual pigments. Photochem Photobiol 62 1-16... 

Nakagawa, M., Iwasa, X, Kikkawa, S., Tsuda, M., and Ebrey, T.G., How vertebrate and invertebrate visual pigments dtfier in their mechanism of photoactivation, Proc. Nad. Acad. Sci. USA, 96,6189,1999. 

Some details about cone cells and invertebrate vision. The biochemistry of retinal cones is less well known but is similar to that of rod cells. Cone pigments are present in the plasma membrane rather than in isolated discs (Fig. 23-40C). Different a, P, and y subunits of transducin are formed in rods and cones.522 Many differences are seen among various invertebrate visual systems. Inositol triphosphate (IP3) and Ca2+ often serve as signals of photoexcitation. G proteins also play prominent roles.522... 

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