Sulfhydryl group modification of photoreceptor G‐protein prevents its light‐induced binding to rhodopsin

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Abstract
The effect of sulfhydryl modification on the light‐induced interaction between rhodopsin and the peripheral GTP‐binding protein of the photoreceptor membrane (G‐protein) has been investigated by time‐resolved near‐infrared light‐scattering and polyacrylamide gel electrophoresis. It has been found that the modification of rhodopsin with the alkylating agent N‐ethylmaleimide (NEM) does not affect its light‐induced interaction with the G‐protein. Modification of G‐protein with NEM or other sulfhydryl agents prevents any light‐induced binding to rhodopsin. Dark‐associatiion of G to the membrane as well as the light‐induced complex with rhodopsin (once formed) is insensitive to NEM.