Application of an invariant spectral form to the visual pigments of crustaceans: implications regarding the binding of the chromophore.

Visual pigment absorption spectra were measured in single photoreceptors of a stomatopod, a crayfish, a hermit crab, and five species of brachyuran crab. All fitted a Mansfield (1985) invariant form for visual pigment, the form also fitted by vertebrate retinal-based visual pigments. This is consistent with a theoretical model based on the structure of visual pigment molecules (Greenberg et al., 1975; Honig et al., 1976) which predicts that spectral bandwidth decreases as lambda max increases. The conformation to the invariant form implies that for any given chromophore bandwidth times lambda max is a constant.