Synthesis and post-translational processing of proenkephalin in light- and dark- adapted chicken retinas

Abstract

Synthesis and post-translational processing of retinal proenkephalin in response to the light or darkness were studied in newly hatched chickens using chromatography, enzymatic digestion (trypsin-carboxypeptidase B) and radioimmunoassay. We found that the concentration of free [Met 5 ]-enkephalin in crude retinal extracts increased with the time in the light and decreased in the dark. This effect was directly dependent on illumination, rather than the consequence of an endogenous circadian rhythm. In contrast, the total amount of cryptic [Met 5 ]-enkephalin (in larger enkephalin-containing polypeptides) remained constant in all stages of the light/dark cycle. We also showed that the relative amounts of cryptic [Met 5 ]-enkephalin stored at different molecular weights remained constant, and that the concentrations of three identified proenkephalin-derived peptides, [Met 5 ]-enkephalin, [Leu 5 ]-enkephalin and [Met 5 ]-enkephalin-Arg 6 -Phe 7 , were higher in the light-adapted than in the dark-adapted retina; but the relative amounts (ratios) of the three proenkephalin-derived peptides stored in the light and in the dark were equal. These data are consistent with the hypothesis that synthesis and processing of proenkephalin proceed at a constant rate and with similar pattern independent of illumination or adaptation, whereas the processed enkephalins are released preferentially in the darkness and accumulated in the light.