Absorption spectra of reconstituted visual pigments of a nocturnal prosimian, Otolemur crassicaudatus

Abstract

Absorption spectra of visual pigments characterize animal vision. The association between absorption spectra and amino acid (aa) sequences of pigments has been well established for the middle- to-long-wave-sensitive (M/LWS) class of cone visual pigments of vertebrates, known as the “five-sites” rule where amino acid residues at the 180th, 197th, 277th, 285th, and 308th sites mostly determine the spectra. For primate M/LWS pigments, however, applicability of the rule is not clear because of the scarcity of absorbance data collected directly from purified pigments. In particular, no prosimian pigment has been examined in vitro. In this study, we reconstituted visual pigments of a nocturnal prosimian, the greater galago ( Otolemur crassicaudatus), which has the M/LWS cone and the rod visual pigments in its retina. The five residues of the galago M/LWS pigment are Ala, His, Tyr, Ala, and Ala, respectively, and its peak absorption spectra ( λ max) was measured to be 539 nm, which is virtually identical to the expected value from the rule (538 nm), showing that the five-sites rule holds for this prosimian. The λ max of the rod visual pigment was measured as 502 nm. Accurate estimate of λ max values is essential in establishing the molecular basis of visual pigment evolution.