Inhibition effect of poly(γ-glutamic acid) on lead-induced toxicity in mice

Detection of Zn2+, Cd2+, Hg2+, and Pb2+ ions through label-free poly-L-glutamic acid

Detection of heavy metal ions in water is important for environmental sustainability and food safety. Current fluorescent sensors interact with metal ions directly through chelation or chemical reactions. Those sensors are expensive to produce and often can detect only one ion at a time. Here we report a fluorescent turn-on sensor that can detect three group IIB metal ions and Pb²⁺ ions through label-free polypeptides in water. In our sensor-polypeptide mixture, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ ions induce helix formation and inter-chain aggregation in poly-L-α-glutamic acid (PGA). The acridinium-based sensor molecules incorporate into the polypeptides and emit strongly with characteristic color for each group IIB ion under UV lamp. By adjusting the size of polypeptides or the length of the side chain carboxyl groups, we can selectively turn off or turn on the sensor emission for Hg²⁺ ions.

Poly-γ-glutamic acid, a bio-chelator, alleviates the toxicity of Cd and Pb in the soil and promotes the establishment of healthy Cucumis sativus L. seedling

Poly-γ-glutamic acid (γ-PGA) can be used as a chemical stabilizer to chelate heavy metals in polluted soils. We investigated the effects of γ-PGA on cucumber seedlings under Cd and Pb stresses. γ-PGA effectively reduced the growth inhibitory effects of Cd and Pb on cucumber seedlings. Cd and Pb absorption in cucumber seedlings was also decreased. Further, γ-PGA decreased the malondialdehyde content, and increased the proline content and the total antioxidant capacity of cucumber seedlings in a dose-dependent manner. Infrared spectral characterization of γ-PGA-Cd and γ-PGA-Pb showed that Cd²⁺ and Pb²⁺ bind to free carboxyl groups on γ-PGA. Furthermore, γ-PGA-Cd and γ-PGA-Pb were degraded by 22.02 and 24.68%, respectively, within 28 weeks. The chelating rate of γ-PGA-Pb and γ-PGA-Cd reached 27.26 and 14.28%, respectively. Further, γ-PGA alleviated the negative effects of Cd and Pb on soil microorganisms. Thus, γ-PGA can effectively reduce the accumulation of heavy metals in crops caused by heavy metal pollution of farmland, and has significant application value.

Biogenic glutamic acid-based resin: Its synthesis and application in the removal of cobalt(II)

Inexpensive biogenic glutamic acid has been utilized to synthesize a cross-linked dianionic polyelectrolyte (CDAP) containing metal chelating ligands. Cycloterpolymerization, using azoisobutyronitrile as an initiator, of N,N-diallylglutamic acid hydrochloride, sulfur dioxide and a cross-linker afforded a pH-responsive cross-linked polyzwitterionic acid (CPZA) which upon basification with NaOH was converted into CDAP. The new resin, characterized by a multitude of spectroscopic techniques as well as Scanning Electron Microscopy (SEM) and Brunauer-Emmett-Teller (BET) analyses, was evaluated for the removal of Co(II) as a model case under different conditions. The adsorption capacity of 137mgg^-1 does indeed make the resin as one of the most effective sorbents in recent times. The resin leverages its cheap natural source and ease of regeneration in combination with its high and fast uptake capacities to offer a great promise for wastewater treatment. The resin has demonstrated remarkable efficiency in removing toxic metal ions including arsenic from a wastewater sample.

Preparation of γ-PGA hydrogels and swelling behaviors in salt solutions with different ionic valence numbers

In this paper, a novel poly γ-glutamic acid (γ-PGA) hydrogel was successfully synthesized by solution polymerization and ethylene glycol diglycidyl ether (EGDE) was used as crosslinker.

Efficient Binding of Heavy Metals by Black Sesame Pigment: Toward Innovative Dietary Strategies To Prevent Bioaccumulation

Black sesame pigment (BSP) was shown to bind lead, cadmium, and mercury at pH 7.0 and to a lower extent at pH 2.0. BSP at 0.05 mg/mL removed the metals at 15 μM to a significant extent (>65% for cadmium and >90% for mercury and lead), with no changes following simulated digestion. The maximum binding capacities at pH 7.0 were 626.0 mg/g (lead), 42.2 mg/g (cadmium), and 69.3 mg/g (mercury). In the presence of essential metals, such as iron, calcium, and zinc, BSP retained high selectivity toward heavy metals. Model pigments from caffeic acid, ferulic acid, and coniferyl alcohol showed lower or comparable binding ability, suggesting that the marked properties of BSP may result from cooperativity of different sites likely carboxy groups and o-diphenol and guaiacyl functionalities. Direct evidence for the presence of such units was obtained by structural analysis of BSP by solid-state Fourier transform infrared spectroscopy and (13)C nuclear magnetic resonance spectroscopy.

Intracellular synthesis of glutamic acid in Bacillus methylotrophicus SK19.001, a glutamate-independent poly(γ-glutamic acid)-producing strain

BACKGROUND

Bacillus methylotrophicus SK19.001 is a glutamate-independent strain that produces poly(γ-glutamic acid) (γ-PGA), a polymer of D- and L-glutamic acids that possesses applications in food, the environment, agriculture, etc. This study was undertaken to explore the synthetic pathway of intracellular L- and D-glutamic acid in SK19.001 by investigating the effects of tricarboxylic acid cycle intermediates and different amino acids as metabolic precursors on the production of γ-PGA and analyzing the activities of the enzymes involved in the synthesis of L- and D-glutamate.

RESULTS

Tricarboxylic acid cycle intermediates and amino acids could participate in the synthesis of γ-PGA via independent pathways in SK19.001. L-Aspartate aminotransferase, L-glutaminase and L-glutamate synthase were the enzymatic sources of L-glutamate. Glutamate racemase was responsible for the formation of D-glutamate for the synthesis of γ-PGA, and the synthetase had stereoselectivity for glutamate substrate.

CONCLUSION

The enzymatic sources of L-glutamate were investigated for the first time in the glutamate-independent γ-PGA-producing strain, and multiple enzymatic sources of L-glutamate were verified in SK19.001, which will benefit efforts to improve production of γ-PGA with metabolic engineering strategies.

In vitro removal of toxic heavy metals by poly(γ-glutamic acid)-coated superparamagnetic nanoparticles

Background:

Chelation therapy involving organic chelators for treatment of heavy metal intoxication can cause cardiac arrest, kidney overload, mineral deficiency, and anemia.

Methods:

In this study, superparamagnetic iron oxide nanoparticles (SPIONs) modified with an edible biopolymer poly(γ-glutamic acid) (PGA) were synthesized by coprecipitation method, characterized and evaluated for their removal efficiency of heavy metals from a metal solution, and simulated gastrointestinal fluid (SGIF).

Results:

Instrumental characterization of bare- and PGA-SPIONs revealed 7% coating of PGA on SPIONs with a spherical shape and an iron oxide spinel structure belonging to magnetite. The particle sizes as determined from transmission electron microscopy images were 8.5 and 11.7 nm for bare- and PGA-SPIONs, respectively, while the magnetization values were 70.3 and 61.5 emu/g. Upon coating with PGA, the zeta potentials were shifted from positive to negative at most of the environmental pH (3–8) and biological pH (1–8), implying good dispersion in aqueous suspension and favorable conditions for heavy metal removal. Batch studies showed rapid removal of lead and cadmium with the kinetic rates estimated by pseudo-second-order model being 0.212 and 0.424 g/mg·min, respectively. A maximum removal occurred in the pH range 4–8 in deionized water and 5–8 in SGIF corresponding to most gastrointestinal pH except for the stomach. Addition of different ionic strengths (0.001–1 M sodium acetate) and essential metals (Cu, Fe, Zn, Mg, Ca, and K) did not show any marked influence on lead removal by PGA-SPIONs, but significantly reduced the binding of cadmium. Compared to deionized water, the lead removal from SGIF was high at all pH with the Langmuir monolayer removal capacity being 98.70 mg/g for the former and 147.71 mg/g for the latter. However, a lower cadmium removal capacity was shown for SGIF (23.15 mg/g) than for deionized water (31.13 mg/g).

Conclusion:

These results suggest that PGA-SPIONs could be used as a metal chelator for clinical treatment of metal poisoning.

Dye adsorption characteristics of magnetite nanoparticles coated with a biopolymer poly(γ-glutamic acid)

Magnetite nanoparticles coated with an anionic biopolymer poly(γ-glutamic acid) (PGA-MNPs) were synthesized and characterized for their methylene blue dye adsorption capability. Both bare- and dye-loaded PGA-MNPs were characterized by FTIR, TEM and VSM measurements, revealing the PGA-MNPs to be superparamagnetic with average particle diameter being 12.4 nm and magnetization value 59.2 emu/g. The synthesized PGA-MNPs were stable in deionized, tap and river waters as well as in acidic and basic media. Redlich-Peterson and Langmuir models precisely described the isotherm and the maximum adsorption capacity was 78.67 mg/g. A pseudo-second-order equation best predicted the kinetics with a maximum adsorption attained within 5 min. Incorporation of sodium or calcium ions reduced the dye adsorption, while a raise in pH enhanced adsorption and a complete desorption occurred at pH 1.0. Dye removal mechanism by PGA-MNPs was probably due to electrostatic interaction through exchange of protons from side-chain α-carboxyl groups on PGA-MNPs surface.