Synthesis and turnover of lipid and protein components of frog retinal rod outer segments

The incorporation and turnover of several lipid precursors in frog retina lipid and protein were studied using biochemical and autoradiographic techniques. Lipid and protein are synthesized on the photoreceptor microsomes from where some migrate to the base of the rod outer segments (ROS) and are incorporated into basal discs. Most of the labeled protein is confined to a discrete group of discs which is displaced apically as newly synthesized unlabeled discs are added. The specific radioactivity of ROS protein is constant throughout this period, which in the present study was determined to be 39 days. Conversely, lipid, once incorporated into the basal discs, diffuses throughout the entire ROS as evidenced by an exponential decline in specific radioactivity. The half-life of ROS lipid is shorter than the renewal rate for protein, suggesting that lipid turns over faster than protein in the ROS.