Protein phosphatase activity is controlled by an inhibitor phosphoprotein in tick salivary glands

Protein phosphatase activity in tick salivary glands was inhibited by heat-stable protein(s) from tick salivary glands as well as by an inhibitor protein from rabbit skeletal muscle. Inhibitor activity was increased after phosphorylation of inhibitor proteins with the catalytic subunit (C) of cyclic AMP-dependent protein kinase and ATP. C inhibited protein phosphatase activity of the partially purified enzyme, while purified cyclic AMP-dependent protein kinase inhibitor protein prevented inhibition of tick salivary gland protein phosphatase by C suggesting that the inhibitor phosphoprotein coelutes with the partially purified enzyme. A soluble heat-stable protein with a molecular weight of approx. 26 kDa was phosphorylated by C, suggesting that a protein phosphatase inhibitor protein similar to inhibitor-1 in mammalian tissue, is present in tick salivary glands.