Classification of Protein- Serine/Threonine Phosphatases: Identification and Quantitation in Cell Extracts

This chapter discusses the classification of protein-serine/threonine phosphatases. These enzymes are divided into two groups—type 1 and type 2, depending on whether they dephosphorylate the β subunit of phosphorylase kinase specifically and are inhibited by nanomolar concentrations, or whether they dephosphorylate the α subunit of phosphorylase kinase preferentially and are insensitive to inhibitors 1 and 2. The type 2 phosphatases can, in turn, be subdivided into three distinct enzymes—PP2A, PP2B, and PP2C by their dependence on divalent cations.