Abstract
Photoreceptor membrane preparation, enriched in rhodopsin content by treatment with 11- cis-retinaldehyde, offer several advantages over detergent-solubilized rhodopsin preparations for the study of the properties of the visual pigment. After a brief description of the chemical composition of the photoreceptor membrane and the role of its phospholipids, chemical modification of the membrane amino groups is reported, leading to the establishment of the chromophoric binding site in native rhodopsin. Through application of the reducing agent sodium borohydride it is demonstrated that the chromophore remains at its original binding site during the conversion to metarhodopsin II, whereas the decay of this substance leads to migration of the chromophore, In the absence of NADPH, which precludes reduction to retinol, 60% of the chromophore remains bound to amino groups of proteins and phospholipids in the membrane. Binding to an amino group in the active site of retinoldehydrogenase takes part in the migrational sequence. Chemical modification of sulfhydryl groups shows that in the absence of detergent no additional SH-groups are exposed upon illumination. This excludes a role of SH-groups in the binding of the chromophore. Proteolytic degradation by pronase of rhodopsin in membrane suspensions is possible without the loss of 500-nm absorbance, which occurs with detergent-solubilized rhodopsin.
Published Version
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