Phosphatase

Phosphatases are a group of enzymes that cleave water storage (hydrolysis) of phosphoric acid esters or phosphoric acid polyphosphates. Run, so to speak by the reverse reaction of a kinase. The best known representatives of this group are named after their pH optimum enzymes acid phosphatase and alkaline phosphatase. Most commonly, the nucleic acid cleaving nucleases, DNA or RNA are depolymerize, i.e., broken down into fragments. They belong to the enzyme class EC 3.1. -. -.

Protein phosphatases

Protein phosphatases remove the protein kinases to amino acid residues (mostly serine and threonine or tyrosine) attached phosphate groups. Both the phosphorylation and dephosphorylation are key components of signal transduction, for example, in the metabolism, where the affected enzymes modulated in its activity thereby. To all involved in the degradation of glycogen enzymes ( phosphorylase kinase, glycogen phosphorylase ) are in the phosphorylated state is active, the synthesis enzyme (UDP - glycogen synthase ), however, inactive. Phosphatases operate these relations into its opposite.

There are 2013 registered nearly 20,000 phosphoproteins with more than 206,000 phosphorylation sites. About 86 percent of the phosphoproteins of mammals are modified to serines, threonines and about twelve percent to about two percent of tyrosines. A little less than four percent of human proteins are protein phosphatases. There are four classes of protein phosphatases, alkaline phosphatases, Ser / Thr- specific, Tyr - specific or dual- specific protein phosphatases.

Alkaline phosphatases are esp. in the intestine before and dephosphorylate not only proteins, including some isoenzymes are inhibited by homoarginine or levamisole and its derivatives, other imidazole.

The Ser / Thr protein phosphatases - specific are further subdivided into type I or type II. Type I phosphatases, such as PP1 can be inhibited by the heat-stable protein inhibitor -1 and inhibitor -2 dephosphorylate and preferably the β - subunit of phosphorylase kinase. Type II phosphatases are distinguished by a Spontaneous activation (subtype A), a Ca2 - dependent or a Mg2 -dependent activation and dephosphorylate preferred the α - subunit of phosphorylase kinase. Ser / Thr- specific phosphatases are inhibited, including through Okadaische acid, calyculin A, cyclosporin, FK -506, microcystin -LR, tautomycin, fostriecin and cantharidin, with varying effectiveness against the various isoforms.

The Tyr- specific protein phosphatases have a conserved catalytic common protein domain. They are inhibited by orthovanadate, inter alia, Peroxovanadate and sodium fluoride.

The dual specificity phosphatases are divided into three groups, with DSP1, DSP 2, DSP4 and DSP5 in Group I, continue DSP6, DSP7, DSP9 and DSP10 in group II and DSP8 and DSP16 in group III, with group III PEST sequences has. Including locating DSP1, DSP2, DSP4 and DSP5 in the nucleus, DSP6, DSP7 and DSP16 in the cytosol, DSP8, DSP9 and DSP10 in both compartments and DSP18 and DSP21 in mitochondria. Dual -specific protein phosphatases are inhibited, inter alia, by orthovanadate.

Serin-/Threonin-spezifische protein phosphatases

There are four classes that are regulated by their location in the cell and by specific inhibitors:

• PP1 ( PP1G plays a role in blood sugar regulation )
• PP2A
• PP2B (synonym: calcineurin )
• PP2C

The first three enzymes show despite different substrate specificity in the catalytic domain of significant homology.

• Protein group
• Phosphatase