Transducing GTPase provides for rapid quenching of the cGMP cascade in rod outer segments

The role of transducin GTPase in rapid cGMP phosphodiesterase quenching was studied by simultaneous registration of GTP hydrolysis and phosphodiesterase activity in the same rod outer segments (ROS) preparation. The results thus obtained allow the conclusion that: phosphodiesterase quenching coincides with transducin-bound GTP hydrolysis independently of ROS concentration; and increase in the ROS concentration results in the acceleration of cascade quenching due to the existence of a GTPase accelerating mechanism in ROS.