The localization of radioactive amino acid taken up into the outer segments of frog ( rana pipiens) rods

Abstract

After injection with tritiated methionine, frogs were sacrificed and the rod outer segments were isolated. It was found (a) that over 70% of the total disintegrations per minute (dis/min) in the outer segments was associated with rhodopsin, (b) that the dis/min in each rhodopsin extract was linearly proportional to the change in the absorbance at 500 nm before and after bleaching, and (c) (by Chromatographic separation of a “crude” rhodopsin extract) that the dis/min were associated mainly with the rhodopsin. Radioautographs of retinas corroborated the data of Young (1967) showing the scleral migration of a discrete band of radioactivity in each photoreceptor outer segment. The present data are consistent with the hypothesis that visual cell outer segments are in a constant state of turnover, and that a major product of this turnover is opsin.