Activation by adenosine 3':5'-monophosphate of a membrane-bound phosphoprotein phosphatase from toad bladder

Adenosine 3':5'-monophosphate (cyclic AMP) caused a decrease in the net rate of incorporation of radioactive phosphate into a specific protein (protein D) in a membrane fraction from toad bladder. Moreover, when the membrane protein was prelabeled with radioactive phosphate, cyclic AMP caused an increase in the net rate of removal of radioactive phosphate from this specific protein. Certain agents were shown to be selective inhibitors of membrane-bound protein D kinase or protein D phosphatase. With the help of these agents, it was concluded that cyclic AMP caused the activation of membrane-bound protein D phosphatase. The present data, together with earlier studies, are compatible with the possibility that the cyclic AMP-induced activation of a membrane-bound phosphoprotein phosphatase in toad bladder, with the consequent dephosphorylation of protein D, may be responsible for the physiological effects of antidiuretic hormone on sodium and/or water transport in this tissue.