| Abstract: | Cyclic GMP phosphodiesterase in frog rod outer segments is activated after flash illumination and is inactivated when left in the dark. ATP reduces the initial peak activity caused by dim flashes (with 50 microM ATP being required for a half-maximal effect) and also accelerates inactivation (with 2 microM ATP being required for a half-maximal effect). An acceleration of inactivation caused by ATP addition is 3-7-fold, depending on the preparation, and ATP effect can be observed even 1 min after a dim flash is given. The accelerated inactivation is also flash intensity-dependent. A low intensity of light causes more rapid inactivation than does a high intensity of light. ATP appears to control phosphodiesterase activity in various ways. |
