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

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