The release of phosphorus from phytate occurs through the sequential cleavage of
phosphate groups from the inositol ring. It was believed that, regardless of the properties
of phytases, the rate of phytate dephosphorylation is limited by the first cleavage of any phosphate group.
The position of the first phosphate group cleaved depends on the specificity of the phytase. The inhibition of dephosphorylation initiation is not related to the enzyme’s mechanism of action but
rather to insufficient phytase activity or low substrate availability.
» Analysis of transformations in the inositol hexaphosphate(IP6) inositol (I) reaction chain shows that the overall dephosphorylation of IP6 limits the removal of the phosphate group from I(1,2,5,6)P4 (the third reaction from the start of phytic acid phosphate bond hydrolysis).
»Reduced nutrient availability in the presence of phytate is not due to phytase activity, but rather to phytate phosphorus anions (IP6-3) binding to positively charged metal ions, amino acids, and proteins..
Phytate is a form of phosphorus storage in plant seeds. As a result of phytase activation during seed germination, phytate releases inorganic phosphate (Pi) for use by growing plants.
Non-ruminant animals do not efficiently digest phytate present in feed due to the low presence of endogenous enzymes in the gastrointestinal tract (GIT).
The term phytate includes various substances defined by the presence of the phytic acid anion (PA).
Enzymes that cleave phytic acid are called myo-inositol hexakisphosphate 3- and 6-phosphohydrolases.
pH is a determining factor affecting the solubility of reaction products. Increasing the pH to 4-5 reduces the solubility of the resulting salts, except for magnesium phytate, which remains soluble at pH 7.5.
In solutions with a pH < 1.1, phytic acid has a neutral charge and remains weakly active. An increase in the pH of the medium to 2 leads to the ionization of three phosphate groups; a further increase in pH results in the loss of the remaining protons.
The phytic phosphorus anion is capable of retaining its negative charge in the gastrointestinal tract and reacting with cations.
In the stomach, lysine, histidine, and arginine, as well as proteins and polypeptides containing these amino acids, can form binary protein-IP6 complexes that inhibit protein digestion.
The binding of phytic acid to positively charged amino acids...
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