OF THE ROLES OF ATP AND GDP IN THE OF PHO TOINDUCED ACTIVATION OF 3',5'-CYCLIC GMP PHOSPHODIESTERASE BY RHODOPSIN FROM VERTEBRATE RETINA PHOTORECEPTOR-MEMBRANES

Using a reconstructed system, composed of washed and illuminated bovin e rod outer segment (ROS) membrane and nonpurified extract from ROS, A TP was shown to activate phosphodiesterase with the same efficiency as GTP at the concentrations down to 2 x 10(-6) M. In the presence of GD P (10(-6) M), the phosphodiesterase activity can be significantly enha nced by ATP (10(-6) M). The initial rate of the phosphodiesterase acti vity in the presence of GTP (10(-6) M) was higher than that in the pre sence of GppNHp at the same concentration.