The significance of protein phosphorylation in regulating the function and activity of protein factors and enzymes is now well established. Analysis of the presence of such phosphorylation, and its attendant effects, is often aided by removal of the protein phosphate groups by phosphatases.
Specificity of Phosphate Removal
Protein phosphorylation can be found on tyrosine, serine and threonine residues. Depending on which phosphatase is chosen, phosphates can be removed from all of these residues, or from a subset thereof. In particular, phosphatases have been characterized as having activity toward serine and threonine residues, or toward tyrosine residues. The specificities of phosphatases sold by NEB toward such residues are given in the table below.
A comparison of protein serine/threonine phosphatase (PSP) to protein tyrosine phosphatase (PTP) specific activity gives a measure of the specificity of the phosphatase. As can be seen in the data presented in the specificity chart below, only one protein phosphatase, TC PTP, is absolutely specific, reacting only with phosphorylated tyrosine residues and not with serine/threonine residues. This enzyme can be used as an absolute tool to distinguish between these two types of phosphorylation. All other listed phosphatases can be used to remove both serine/threonine and tyrosine phosphorylation. It should be noted that despite their dual specificities, these latter phosphatases display different preferences: Lambda Protein Phosphatase and Protein Phosphatase 1 have greater reactivity against phospho-serine/threonine residues, Calf Intestinal Phosphatase shows a preference for phosphotyrosine residues, and Antarctic Phosphatase has similar activity on both types of phosphorylation (1).
- Barshevsky, T. (2008) New England Biolabs, unpublished results.