TRANSDUCTIN CONTROLS LIGHT-INDUCED POLYPH OSPHOINOSITIDE HYDROLYSIS IN BOVINE RETINAL RODS

The pronounced increase in light-induced phosphatidylinositol 4,5-bisp hosphate hydrolysis in rod outer segment (ROS) membranes was shown to occur upon addition of 100 muM GTP into the medium. Light sensitivity of hydrolysis decreased after treatment of ROS membranes with cholera or pertussis toxins. The removal of disc membrane peripheral protein b y hypotonic washing actually eliminated both light- and GTP-dependence of the process, which can be restored by adding the ROS lysate of pur ified rod G-protein transducin. Immunoblot analysis. with G-protein mo noclonal antibodies did not show any other G-proteins besides transduc in in ROS membranes. Thus, retinal transducin plays the role of a coup ling factor between rhodopsin bleaching and phosphoinositide hydrolysi s in the ROS membrane system.