Differential effects of puromycin on the incorporation of precursors of rhodopsin in bovine retina.

Bovine retinas incubated in vitro sustain the synthesis of opsin and rhodopsin as monitored by the incorporation of labeled leucine, mannose, and glucosamine. Puromycin, an inhibitor of protein synthesis, effectively blocks the incorporation of leucine and mannose into opsin and rhodopsin of rod outer segments. However, the incorporation of glucosamine into opsin and rhodopsin is not immediately blocked. Instead, it continues for a time suggesting not only core oligosaccharide synthesis but also the secondary glycosylation of a pool of preformed opsin which is thought to be transiently accumulated in the photoreceptor Golgi complex. Galactose, not normally found in rhodopsin, is also incorporated into both opsin and rhodopsin. This incorporation appears to be completely insensitive to puromycin, suggesting that it may occur in the rod outer segments involving only preexisting glycoproteins.