Purple acid phosphatases
Encyclopedia
Purple acid phosphatase
s (PAPs) are metalloenzymes that hydrolyse phosphate esters and anhydrides under acidic condition. In their oxidised form, PAPs in solution are purple in colour. This is due to the presence of a dinuclear iron centre, to which a tyrosine
residue is connected via a charge transfer
. This metallic centre is composed of Fe3+ and M, where M is Fe3+, Zn
2+, Mg
2+ or Mn
2+. The conserved Fe3+ is stabilised 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.
PAPs are highly conserved within eukaryotic species, with >80% amino acid
homology
in mammalian PAPs, and >70% sequence homology in PAPs of plant origin. 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. 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.
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.
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 . This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their...
s (PAPs) are metalloenzymes that hydrolyse phosphate esters and anhydrides under acidic condition. In their oxidised form, PAPs in solution are purple in colour. This is due to the presence of a dinuclear iron centre, to which a tyrosine
Tyrosine
Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group...
residue is connected via a charge transfer
Charge transfer complex
A charge-transfer complex or electron-donor-acceptor complex is an association of two or more molecules, or of different parts of one very large molecule, in which a fraction of electronic charge is transferred between the molecular entities. The resulting electrostatic attraction provides a...
. This metallic centre is composed of Fe3+ and M, where M is Fe3+, Zn
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
2+, Mg
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
2+ or Mn
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
2+. The conserved Fe3+ is stabilised in the ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
form, whereas M may undergo reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
. 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.
PAPs are highly conserved within eukaryotic species, with >80% amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
homology
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
in mammalian PAPs, and >70% sequence homology in PAPs of plant origin. 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. 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.
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
Tartrate resistant acid phosphatase
Tartrate-resistant acid phosphatase or acid phosphatase 5, tartrate resistant is a glycosylated monomeric metalloenzyme expressed in mammals. It has a molecular weight of approximately 35kDa, a basic isoelectric point , and optimal activity in acidic conditions. TRAP is synthesized as latent...
(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.