Phytase

A phytase (myo-inositol hexakisphosphate phosphohydrolase) is any type of

In 1991 BASF began to sell the first commercial phytase produced in A. niger under the trademark Natuphos which was used to increase the nutrient content of animal feed.^[6]

In 1999 Escherichia coli bacterial phytases were identified as being more effective than A. niger fungal phytases.^[6][10][11] Subsequently, this led to the animal feed use of this new generation of bacterial phytases which were superior to fungal phytases in many aspects.^[6]

Classes

Four distinct classes of phytase have been characterized in the literature: histidine acid phosphatases (HAPS), beta-propeller phytases (BPPs), purple acid phosphatases (PAPs),^[2] and most recently, protein tyrosine phosphatase-like phytases (PTP-like phytases).^[12]

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.^[1] 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).^[2] 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.^[13] HAPs have also been overexpressed in several transgenic plants as a potential alternative method of phytase production for the animal feed industry^[14] and very recently, the HAP phytase gene from E. coli has been successfully expressed in a transgenic pig.^[15]

β-propeller phytases

β-propeller phytases make up a recently discovered class of phytase. These first examples of this class of enzyme were originally cloned from Bacillus species,^[2] but numerous microorganisms have since been identified as producing β-propeller phytases. The three-dimensional structure of β-propeller phytase is similar to a propeller with six blades. Current research suggests that β-propeller phytases are the major phytate-degrading enzymes in water and soil, and may play a major role in phytate-phosphorus cycling.^[16]

Purple acid phosphatases

A phytase has recently been isolated from the cotyledons of germinating soybeans that has the active site motif of a purple acid phosphatase (PAP). This class of metalloenzyme has been well studied and searches of genomic databases reveal PAP-like sequences in plants, mammals, fungi, and bacteria. However, only the PAP from soybeans has been found to have any significant phytase activity. The three-dimensional structure, active-site sequence motif and proposed mechanism of catalysis have been determined for PAPs.^{[citation needed]}

Protein tyrosine phosphatase-like phytases

Only a few of the known phytases belong to a

Phytic acid has six phosphate groups that may be released by phytases at different rates and in different order. Phytases hydrolyze phosphates from phytic acid in a stepwise manner, yielding products that again become substrates for further hydrolysis. Most phytases are able to cleave five of the six phosphate groups from phytic acid. Phytases have been grouped based on the first phosphate position of phytic acid that is hydrolyzed. The Enzyme Nomenclature Committee of the International Union of Biochemistry recognizes three types of phytases based on the position of the first phosphate hydrolyzed, those are 3-phytase (EC 3.1.3.8), 4-phytase (EC 3.1.3.26), and 5-phytase (EC 3.1.3.72). To date, most of the known phytases are 3-phytases or 4-phytases,^[21] only a HAP purified from lily pollen^[22] and a PTP-like phytase from Selenomonas ruminantium subsp. lactilytica^[20] have been determined to be 5-phytases.

Biological relevance

Phytic acid and its metabolites have several other important roles in Eukaryotic physiological processes. As such, phytases, which hydrolyze phytic acid and its metabolites, also have important roles. Phytic acid and its metabolites have been implicated in DNA repair, clathrin-coated vesicular recycling, control of neurotransmission and cell proliferation.^[25][26][27] The exact roles of phytases in the regulation of phytic acid and its metabolites and the resulting role in the physiological processes described above are still largely unknown and the subject of much research.

Phytase has been reported to cause hypersensitivity pneumonitis in a human exposed while adding the enzyme to cattle feed.^[28][29]

Agricultural and industrial uses

Phytase is produced by bacteria found in the gut of

• 4-phytase
• 3-phytase
• 5-phytase
• Phytic acid

References