Dynamic Interconversion of Receptors Involving Dephosphorylation by Protein Tyr(P) and Ser(P)/Thr(P) Phosphatases

Dynamic cycling of receptors between phosphorylated and dephosphorylated forms is used as a mechanism for regulation of various physiological events. Historically, the first enzyme responsible for the interconversion of another enzyme between active and inactive states was called “PR enzyme by Cori and Cori who discovered it in 1945. The chapter reviews experimental data available through mid-1986 on the dephosphorylation of different receptors with ³²P or the effects of compounds added to inhibit the phosphatases. The high affinity for Zn²⁺ provided a basis for purification involving metal-chelate chromatography. Few investigators study the dephosphorylation of proteins, a process which as a regulatory device can be considered equivalent to phosphorylation. Cycling of proteins between phospho forms occurs constantly from the action of protein kinases (PKs) and protein phosphatases that are present in cells as regulated enzymes with their activities strongly repressed. Specific inhibition and substrate specificity are still the most dependable and widely applied tests to distinguish various phosphatases.