Editing Protein phosphatase (section)

==Mechanism==
Phosphorylation involves the transfer of phosphate groups from [[adenosine triphosphate|ATP]] to the enzyme, the energy for which comes from hydrolysing ATP into [[Adenosine diphosphate|ADP]] or [[Adenosine monophosphate|AMP]]. However, dephosphorylation releases phosphates into solution as free ions, because attaching them back to ATP would require energy input.

Cysteine-dependent phosphatases (CDPs) catalyse the hydrolysis of a phosphoester bond via a phospho-cysteine intermediate.<ref>{{cite journal | vauthors = Barford D | title = Molecular mechanisms of the protein serine/threonine phosphatases | journal = Trends in Biochemical Sciences | volume = 21 | issue = 11 | pages = 407–12 | date = November 1996 | pmid = 8987393 | doi = 10.1016/S0968-0004(96)10060-8 }}</ref>
[[Image:PhosphataseMech.svg|thumb|300px|Mechanism of Tyrosine dephosphorylation by a CDP]]
The free [[cysteine]] [[nucleophile]] forms a bond with the [[phosphorus]] atom of the phosphate moiety, and the P-O bond linking the phosphate group to the tyrosine is protonated, either by a suitably positioned acidic [[amino acid]] residue (Asp in the diagram below) or a water molecule. The phospho-cysteine intermediate is then hydrolysed by another water molecule, thus regenerating the active site for another dephosphorylation reaction.

Metallo-phosphatases (e.g. PP2C) co-ordinate 2 [[catalytically essential metal ion]]s within their active site. There is currently some confusion of the identity of these metal ions, as successive attempts to identify them yield different answers. There is currently evidence that these metals could be [[magnesium in biology|magnesium]], [[manganese in biology|manganese]], [[iron in biology|iron]], [[zinc in biology|zinc]], or any combination thereof. It is thought that a hydroxyl ion bridging the two metal ions takes part in [[nucleophile|nucleophilic]] attack on the [[phosphorus]] ion.