The Visual Pigments

Absorption Spectra of Isolated Single Frog Retinal Rods and Cones

¹ Biophysical Research Laboratory, Eye and Ear Hospital, University of Pittsburgh School of Medicine, Pittsburgh, Pa.

The visual pigment complex within a single retinal rod and. cone can be studied, by microspectrophotometry in order to identify the pigments during the light < -- > dark reactions. Specimen areas in the rods and cones of the order 2 µ² were scanned at relatively low magnifications from 340 to 900 mµ. Freshly isolated frog (Rana pipiens) retinal rods and cones toere rapidly scanned with the microspectrophotometer at 22° C. The retinal rods shoioed a broad absorption peak near 500 mµ, typical of extracted frog rhodopsin. However, additional peaks at 380, 440, 480, and 515 mµ, were also observed. Some of these absorption peaks may he products of bleaching. Upon light bleaching, the 380 mµ, peak substantially increases, whereas the other absorption peaks diminish. These spectral changes upon light bleaching are accompanied by structural changes in the retinal rod. The shifts in spectral peaks indicate a mixture of isomers which may be formed upon light bleaching. In addition, these studies shotu that rhodopsin is evenly distributed throughout the outer segment of the retinal rod. From the absorption data and the volume of the retinal rod, the concentration of rhodopsin ivas calculated to be 3 x 10⁹ molecules. The retinal cones show general absorption throughout the visible range, with major peaks near or at 420, 470, 540, 570, 610, 660, and 690 mµ,. These and. other experimental data are presented and discussed.