Synaptojanin is a protein involved in vesicle uncoating in neurons. This is an important regulatory lipid phosphatase. It dephosphorylates the D-5 position phosphate from Phosphatidylinositol (3,4,5)-trisphosphate and Phosphatidylinositol (4,5)-bisphosphate. It belongs to family of 5-phosphatases, which are structurally unrelated to D-3 inositol phosphatases like PTEN.
As of late 2007, only one structure has been solved for this class of enzymes, with the PDB accession code 2HF2.
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In enzymology, a sugar-phosphatase (EC 3.1.3.23) is an enzyme that catalyzes the chemical reaction
sugar phosphate + H2O sugar + phosphate
Thus, the two substrates of this enzyme are sugar phosphate and H2O, whereas its two products are sugar and phosphate.
This enzyme belongs to the family of hydrolases, specifically those acting on phosphoric monoester bonds. The systematic name of this enzyme class is sugar-phosphate phosphohydrolase.
In enzymology, a sucrose-phosphatase (EC 3.1.3.24) is an enzyme that catalyzes the chemical reaction
sucrose 6F-phosphate + H2O sucrose + phosphate
Thus, the two substrates of this enzyme are sucrose 6F-phosphate and H2O, whereas its two products are sucrose and phosphate.
This enzyme belongs to the family of hydrolases, specifically those acting on phosphoric monoester bonds. The systematic name of this enzyme class is sucrose-6F-phosphate phosphohydrolase. Other names in common use include sucrose 6-phosphate hydrolase, sucrose-phosphate hydrolase, sucrose-phosphate phosphohydrolase, and sucrose-6-phosphatase. This enzyme participates in starch and sucrose metabolism.
Purple acid phosphatases (PAPs) (EC 3.1.3.2) are metalloenzymes that hydrolyse phosphate esters and anhydrides under acidic condition.[1][2] In their oxidised form, PAPs in solution are purple in colour. This is due to the presence of a dinuclear iron centre,[3] to which, a tyrosine residue is connected via a charge transfer.[4] This metallic centre is composed of Fe3+ and M, where M is Fe3+, Zn2+, Mg2+ or Mn2+. The conserved Fe3+ is stabilized in the ferric form, whereas M may undergo reduction. Upon treatment with mild reductants, PAPs are converted to their enzymatically active, pink form. Treatment with strong reducing agents dissociates the metallic ions, and renders the enzyme colourless and inactive.[5]
PAPs are highly conserved within eukaryotic species, with >80% amino acid homology in mammalian PAPs,[6] and >70% sequence homology in PAPs of plant origin.[7] However sequence analysis reveals that there is minimal homology between plant and mammal PAPs (<20%), except for the metal-ligating amino acid residues which are identical.[8] The metallic nucleus of PAPs also varies between plants and mammals. Mammalian PAPs which have been isolated and purified have, to this point, been composed exclusively of iron ions, whereas in plants the metallic nucleus is composed of Fe3+ and either Zn2+ or Mn2+. PAPs have also been isolated in fungi, and DNA sequences encoding for possible PAPs have been identified in prokaryotic organisms, such as in Cyanobacteria spp. and Mycobacteria spp.[9]
Currently there is no defined nomenclature for this group of enzymes, and a variety of names exists. These include purple acid phosphatase (PAP), uteroferrin (Uf), type 5 acid phosphatase (Acp 5) and tartrate resistant acid phosphatase (TRAP, TRACP, TR-AP). There is, however, a consensus in the literature that purple acid phosphatase (PAP) relates to those found in non-mammalian species and tartrate resistant acid phosphatase (TRAP) to those found in mammalian species.
Uteroferrin, bovine spleen PAP and tartrate resistant acid phosphatase all refer to mammalian PAPs, whereby research on PAPs expressed in various tissues diverged. Subsequent research has proven that all of these enzymes are the same entity.[10][11]
Individual PTPs may be expressed by all cell types or their expression may be strictly tissue specific. Most cells express 30% to 60% of all the PTPs, however hematopoietic and neuronal cells express a relatively higher number of PTPs in comparision to other cell types. T cells and B cells of hematopoietic origin express around 60 to 70 different PTPs. The expression of several PTPS is restricted to hematopoietic cells, for example LYP, SHP1, CD45 and HePTP.[2]
On the basis of the primary structure of their catalytic domains, PTPs are divided into four distinct classes:[1]
The class I PTPs, are the the largest group of PTPs with 99 members which can be further subdivided into 38 classical PTPs and 61 VH-1 like or dual specific phosphatases (DSPs). The class I classical PTPs can be futher subdivided into 21 receptor and 17 non receptor type PTPs. The DSPs can also be further subdivided, in this case into 7 subfamilies made up of 11 MAPK phosphatases (MPKs), 3 Slingshots, 3 PRLs, 4 CDC14s, 19 atypical DSPs, 5 Phosphatase and tensin homologs (PTENs) and 16 Myotubularins. The class II PTPs contain only one member, low-molecular-weight phosphotyrosine phosphatase (LMPTP). The Class III PTPs contains three members, CDC25 A, B and C and the class IV PTPs contains four members, Eya1-4. Links to all 107 members of the protein tyrosine phosphatase family can be found in the template at the bottom of this article.
Together with tyrosine kinases, PTPs regulate the phosphorylation state of many important signalling molecules, such as the MAP kinase family.
PTPs are increasingly viewed as integral components of signal transduction cascades, despite little studied and ill-understood compared to Tyrosine Kinases.
PTPs have been implicated in regulation of many cellular processes, including, but not limited to:
Cell growth
Cellular differentiation
Mitotic cycles
Oncogenic transformation
Protein tyrosine phosphatases (PTPs) are a group of enzymes that remove phosphate groups from phosphorylated tyrosine residues on proteins.
As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes 1D8H, 1D8I, 1I9S, 1I9T, and 1YN9.