In-gel protein phosphatase assays and other useful methods for the detection of protein phosphatase activities

Intracellular signaling is governed by protein phosphorylation and dephosphorylation catalyzed by protein kinases and protein phosphatases, respectively. Since there is growing evidence that a variety of protein phosphatases are involved in the pathogenesis of various diseases, protein phosphatases have recently been the focus of intense research interest, not only in basic biology but also in clinical medicine. In the process of these studies, analytical methods for protein phosphatases will be of increasing importance. A major bottleneck in protein phosphatase assays is the selection and preparation of an efficient substrate for the phosphatase to be assayed. To circumvent this difficulty, a variety of protein phosphatase substrates have been devised during the development of novel assay techniques by which protein phosphatase activities can be readily detected. In this review, we focus on the methodology for detecting protein phosphatase activities, with special emphasis on in-gel protein phosphatase assays and related techniques. The utility and limitations of these methods are also discussed.