Zinc Phytate Research Articles

Influence of phytic acid on zinc phosphate cement.

The influence of phytic acid on the properties of zinc phosphate cement was studied by adding 2-13 wt% phytic acid to the liquid. Improved mechanical strength and stability were found for some cements prepared from commercial powders when liquids with increased phytic acid content were used. The results indicate that the formation of increased amounts of zinc phytate has a favorable effect on the properties of zinc phosphate cement.

Zinc tolerance and the binding of zinc as zinc phytate in Lemna minor. X-ray microanalytical evidence

Summary Electron probe X-ray microanalysis of fracture faces of quench frozen hydrated bulk samples of Lemna minor fronds exposed to high levels of Zn (300 µM) has shown the presence of globular deposits up to 1 µm in diameter containing Zn, K and P in parenchyma cells of mature fronds, and Zn, K, Mg and P in immature parenchyma cells of daughter fronds (or turions). Although this method of direct analysis of bulk samples does not lend itself to a quantitative comparison of number and composition of globules in Zn-tolerant and Zn-sensitive clones of Lemna minor , it has the advantages of simplicity of specimen preparation, rapid detection of Zn-P-containing globules, and avoidance of diffusional artifacts. Comparisons with prepared K Mg phytate and Zn standards, and additional data obtained by X-ray microanalysis of freeze-substituted thin sections, established the elemental proportions of Zn, Mg, K and Ca relative to P, which indicate that generally up to 8 (molar ratio of Zn to phytic acid = 4) and sometimes up to 12 (molar ratio of Zn to phytic acid = 6) valencies can be occupied by Zn and up to 4 by K and/or Mg. Some of the Ca that appears to be associated with globules may result from elemental redistribution during the process of freeze-substitution especially when Ca oxalate crystals are present in neighbouring raphide cells. X-ray microanalysis provided evidence for the absence of Zn from these raphides.

NMR and ESR studies of interactions among divalent cations, phytic acid, and N-acetyl-amino acids

Ion-selective electrode potentiometry, 13C and 31P nuclear magnetic resonance (NMR) and electron spin resonance (ESR) techniques have been utilized to study the independent and mutual interactions of divalent cations (zinc, copper, and calcium ions), phytic acid, and N-acetylhistidine or N-acetylglutamate. In pH 7.00 copper phytate and calcium phytate solutions (1 mM divalent cation, 10 mM phytate), the preferential phytate binding sites for calcium and copper(II) ions appear to be the P5 phosphate group, or between the P5 phosphate group and the P4 or P6 phosphate groups, with the phytate molecule in the 5 equatorial/1 axial conformation. An insoluble zinc phytate complex with a 4:1 zinc ion:phytate molar ratio slowly precipitated from the pH 7.00 zinc phytate solution (1 mM zinc ions, 10 mM phytate). Soluble ternary complexes involving phytate, N-acetylhistidine, and calcium, copper(II), or zinc ions may exist at pH 7.00. There was no evidence of ternary phytate-divalent cation-N-acetylglutamate complexes existing at pH 7.00.

Binding differences of Zn(II) and Cu(II) ions with phytate

Binding differences have been observed between Zn(II) ions and Cu(II) ions with phytate. In pH 7.00 solutions containing 10 mM phytate, 1 mM Cu(II) or Zn(II) ions, and 0–0.15 M NaCl, all of the Cu(II) ions were bound by phytate as soluble species, whereas an insoluble zinc phytate complex slowly precipitated from solution. More phytate precipitated after 3 hr from zinc phytate solutions of higher ionic strength than from the solutions of lower ionic strength. After 48 hr, the ionic strength of the zinc phytate solution did not affect the amount of phytate precipitated. The zinc: phytate molar ratio in the precipitates collected after 3 hr was 4:1. This binding ratio decreased to 3.5:1 in precipitates collected after 24 and 48 hr. Chemical shift changes in the 31P NMR spectra of pH 7.00 phytate and zinc phytate solutions, as functions of ionic strength, provided an explanation for these observations. Arguments are presented to support the proposition that Zn(II) ions preferentially bind the 5 axial/1 equatorial phytate conformer in pH 7.00 solutions containing 10 mM phytate and 1 mM Zn(II) ions.

Deposition of Zinc Phytate in Globular Bodies in Roots of Deschampsia caespitosa Ecotypes; a Detoxification Mechanism?

Summary Electron probe X-ray microanalysis of freeze-substituted thin sections (non-aqueous specimen preparation) has shown the presence of Zn, K, Mg and P in globular bodies up to 1 μm in diameter within small vacuoles of cortical cells in the elongation zone of root tips of Deschampsia caespitosa plants which had been exposed to toxic concentrations of Zn. Comparison of the spectra with those obtained from standards prepared from phytic acid and known quantities of various metal ions, strongly suggests that the globular bodies consist of phytate with Zn, Mg and K present in constant proportions relative to P. These proportions depend on Zn treatment and on whether the ecotype is sensitive or tolerant to Zn. In globules of the tolerant ecotype exposed to 1000μM Zn, up to six valencies are occupied by Zn, four by Mg and the remaining two by K, which indicates that the phytate consists of myo-inositol hexakisphosphate. The unusually high Zn content (20.1 % by weight) of the globules in the cortical cells of these roots suggests that they may act as a mechanism for detoxification of Zn, especially in the Zn tolerant ecotype of Deschampsia caespitosa .

Heats of precipitation of zinc phytate

The heat of precipitation for the reaction of zinc ion with the phytate ion in aqueous solution has been determined. The reaction is endothermic. From the value of the equilibrium constant associated with the reaction, the entropy change has been calculated. The entropy change is large and positive. This is consistent with the view that when zinc reacts with phytate to form solid zinc phytate there is an increase in the number of particles in the system.

Availability to the Chick of Zinc· Phytate Complexes Isolated from Oil Seed Meals by an in vitro Digestion Method

Studies were made of the form in which zinc was found after digestion in vitro of oil seed meals which varied in zinc availability in vivo. Regardless of in vivo differences, the zinc of two sesame meals and one safflower meal was present in an insoluble, nondialyzable Ca·Mg·Zn·phytate complex at intestinal pH. The zinc was little available to the chick as shown by low uptake of 65Zn from the labeled complexes. For a soybean meal digest, about 75% of the extracted zinc, 40% of the phytate phosphorus and 90% of the calcium and magnesium were soluble at intestinal pH. About 50% of the zinc was dialyzable in a 4-hour period. The zinc of the soybean meal digest was bound in a water-soluble and dialyzable complex which was more stable than zinc phytate. The binding agent was termed a “carrier.” The addition of soluble digestion products of the sesame or safflower meals to the insoluble labeled Ca·Mg·65Zn·phytate complexes did not promote dialysis of 65Zn, but the “carrier” rendered 15 to 29% of the 65Zn dialyzable at intestinal pH. Three isolated soy proteins contained low or no “carrier” properties.

Dietary Metal-complexing Agents and Zinc Availability in the Rat

The growth rate of weanling rats was used to determine the effects of phytate, calcium and ethylenediaminetetraacetate (EDTA) upon the physiological availability of zinc. Phytate decreased availability and the effect was augmented by excess dietary calcium. Calcium had no effect in the absence of phytate so that its effect must be mediated through an interaction with phytate. EDTA increased zinc availability when the diet contained phytate but had no significant effect upon the growth rate in the absence of phytate. In vitro experiments showed that zinc phytate is highly insoluble at the pH range encountered in the small intestine. Addition of calcium to the medium produced an even more insoluble complex containing zinc, calcium and phytate. The results suggest that the formation of such complexes with phytate is the mechanism whereby zinc is made less available and the more complete precipitation of zinc in the presence of calcium explains the effect of excess calcium. In vitro studies with intestinal strips and 65Zn showed that zinc uptake was progressively decreased as the ratio of calcium to phytate was increased. This effect was counteracted in part by the addition of EDTA. It appears that EDTA increases zinc availability by competing with phytate and forming a soluble complex which allows absorption across membranes.