Flash Photolysis of Rhodopsin in the Retina

Abstract

IT has long been suspected that the ability of rhodopsin to sensitize vertebrate retinal rods to visible light depends in some way upon the rapid and conspicuous fading which the purple photopigment undergoes when it is illuminated¹. If so, some part of the bleaching process that is undergone by photochemically excited rhodopsin molecules must be very rapid, for vertebrate eyes respond very quickly to flashes of light. Indirect evidence for the existence of fast reactions in the bleaching of rhodopsin has been provided by Wald, Durell and St. George², who found that two successive unstable intermediates, lumi- and meta-rhodopsin, were formed when dry gelatin films or frozen solutions containing extracted rhodopsin were illuminated and examined spectro-photometrically. These authors suggested a scheme-for the photochemical decomposition of rhodopsin shown in Fig. 1, in which they believed that all reactions except (3) would be fast enough in vivo to be able to play some part in the excitation of living rods.