Photoproducts of rhodopsin bleaching in the isolated, perfused frog retina

Abstract

Sequential absorption spectra of decaying rhodopsin photoproducts have been recorded in isolated, perfused frog retinas following brief, intense light flashes. Two photoproduct peaks have been observed, with λ max at 387 nm and 462–475 nm. The behavior of these peaks has been studied as a function of pH, temperature, and illumination with near-ultraviolet light. The 387 nm peak consists of metarhodopsin II and free all- trans retinal, while the 462–475 nm peak is pararhodopsin. Photoproduct decay in the frog retina is similar to that previously described in intact rat and rabbit retinas, save that the transformation of metarhodopsin II to pararhodopsin is much faster in the frog at comparable temperatures. Photoproduct transitions in the intact frog retina are less complex than those previously observed in digitonin extracts of rhodopsin, or in suspensions of retinal outer segments in hypertonic sucrose solutions. When isolated, perfused frog retinas are strongly bleached in white light, about 15 per cent of the rhodopsin regenerates over 30–50 min following the bleach. Regeneration is prevented if the ultraviolet spectrum is filtered from the bleaching light. It therefore requires prior photoisomerization of the prosthetic group.