Phosphatase

A phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group (see dephosphorylation). This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their substrates by using energetic molecules like ATP. A common phosphatase in many organisms is alkaline phosphatase. Another large group of proteins present in archaea, bacteria, and eukaryote exhibits deoxyribonucleotide and ribonucleotide phosphatase or pyrophosphatase activities that catalyse the decomposition of dNTP/NTP into dNDP/NDP and a free phosphate ion or dNMP/NMP and a free pyrophosphate ion. Another very important group of phosphatases involved in cellular signalling are collectively called the protein phosphatase, which removes a phosphate group from the phosphorylated amino acid (Ser, Thr or Tyr) of the substrate protein. Protein phosphorylation is a common posttranslational modification of protein catalyzed by protein kinases, and protein phosphatases reverse the effect, permitting switch-like regulation of phosphorylated substrates. The protein pseudophosphatases form part of the larger phosphatase family, and in most cases are thought to be catalytically inert, instead functioning as phosphate-binding proteins, integrators of signalling or subcellular traps in cells. Examples of protein phosphates containing phosphatase and pseudophosphatase domains linked in tandem have been described, conceptually similar to the kinase and pseudokinase domain polypeptide structure of the JAK pseudokinases.

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