Phytase

A phytase (myo-inositol hexakisphosphate phosphohydrolase) is any type of phosphatase enzyme that catalyzes the hydrolysis of phytic acid (myo-inositol hexakisphosphate) – an indigestible, organic form of phosphorus that is found in grains and oil seeds – and releases a usable form of inorganic phosphorus. While phytases have been found to occur in animals, plants, fungi and bacteria, phytases have been most commonly detected and characterized from fungi.

Classes

Four distinct classes of phytase have been characterized in the literature: histidine acid phosphatases (HAPS), B-propeller phytases, purple acid phosphatases, and most recently, protein tyrosine phosphatase-like phytases (PTP-like phytases).

Histidine acid phosphatases (HAPs)

Most of the known phytases belong to a class of enzyme called histidine acid phosphatases (HAPs). HAPs have been isolated from filamentous fungi, bacteria, yeast, and plants. All members of this class of phytase share a common active site sequence motif (Arg-His-Gly-X-Arg-X-Pro) and have a two-step mechanism that hydrolyzes phytic acid (as well as some other phosphoesters). The phytase from the fungus Aspergillus niger is a HAP and is well known for its high specific activity and its commercially marketed role as an animal feed additive to increase the bioavailability of phosphate from phytic acid in the grain-based diets of poultry and swine. HAPs have also been overexpressed in several transgenic plants as a potential alternative method of phytase production for the animal feed industry and very recently, the HAP phytase gene from E. coli has been successfully expressed in a transgenic pig.

4-phytase

In enzymology, a 4-phytase (EC 3.1.3.26) is an enzyme that catalyzes the chemical reaction

Thus, the two substrates of this enzyme are myo-inositol hexakisphosphate and H₂O, whereas its two products are 1D-myo-inositol 1,2,3,4,5-pentakisphosphate 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 myo-inositol-hexakisphosphate 6-phosphohydrolase. Other names in common use include 6-phytase (name based on 1L-numbering system and not 1D-numbering), phytase, and phytate 6-phosphatase. This enzyme participates in inositol phosphate metabolism.

References

5-phytase

In enzymology, a 5-phytase (EC 3.1.3.72) is an enzyme that catalyzes the chemical reaction

Thus, the two substrates of this enzyme are myo-inositol hexakisphosphate and H₂O, whereas its two products are 1L-myo-inositol 1,2,3,4,6-pentakisphosphate 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 myo-inositol-hexakisphosphate 5-phosphohydrolase.

Prevalence

Of the hundreds of phytase enzymes that have been characterized in the literature, only two have been characterized as 5-phytases. A histidine acid phosphatases purified from lily pollen and a protein tyrosine phosphatase-like phytase from Selenomonas ruminantium subsp. lactilytica were both found to have specificity for the 5-phosphate position of myo-inositol hexakisphosphate.

Structural studies

As of late 2007, only the phytase purified from lily pollen had its structure solved, with PDB accession codes 1U24, 1U25, 1U26, 2B4O, 2B4P, and 2B4U.