Cyanopsin, a Visual Pigment of Retinal Origin

Abstract

IN 1953, Wald¹ reported in vitro synthesis of a new photosensitive pigment. This was made by combining the opsin obtained from extracts of chicken iodopsin² with 11-cis retinene₂ in place of the native 11-cis retinene₁. The pigment thus formed absorbed maximally at 620 nm instead of the native 562 nm, and was named cyanopsin. It had a number of properties which made it a good candidate for a visual pigment, although it had not been extracted directly from any retina and could not therefore be associated convincingly with the visual system of any animal. Such a pigment has yet to be extracted from a retina; but, in addition to discovering whether a pigment like cyanopsin exists in nature, and, in particular, in cones, it would be satisfying to observe whether there exists a natural iodopsin in situ to which the 620 pigment is related by a simple change of prosthetic group.