One of the most common post-translational modifications is the phosphorylation of proteins at serine, threonine and/or tyrosine residues. Indeed, genetic engineering and mutagenesis studies have also enabled the production of intrinsically activated mutants which biologically “mimic” the phosphorylated form of the protein. Along with protein phosphorylation, the cell needs to be able to reverse the activated/non-activated form of the protein via the removal of the phosphate group. Protein phosphatases play such a role in the cell and are responsible for removing phosphate groups from serine/threonine and tyrosine residues.