Presence Of PGA Research Articles

The Blending of Poly(glycolic acid) with Polycaprolactone and Poly(l-lactide): Promising Combinations.

Poly(glycolic acid) (PGA) holds unique properties, including high gas barrier properties, high tensile strength, high resistance to common organic solvents, high heat distortion temperature, high stiffness, as well as fast biodegradability and compostability. Nevertheless, this polymer has not been exploited at a large scale due to its relatively high production cost. As such, the combination of PGA with other bioplastics on one hand could reduce the material final cost and on the other disclose new properties while maintaining its “green” features. With this in mind, in this work, PGA was combined with two of the most widely applied bioplastics, namely poly(l-lactide) (PLLA) and poycaprolactone (PCL), using the melt blending technique, which is an easily scalable method. FE-SEM measurements demonstrated the formation of PGA domains whose dimensions depended on the polymer matrix and which turned out to decrease by diminishing the PGA content in the mixture. Although there was scarce compatibility between the blend components, interestingly, PGA was found to affect both the thermal properties and the degradation behavior of the polymer matrices. In particular, concerning the latter property, the presence of PGA in the blends turned out to accelerate the hydrolysis process, particularly in the case of the PLLA-based systems.

Impact of Organic Matter on Microbially-Mediated Reduction and Mobilization of Arsenic and Iron in Arsenic(V)-Bearing Ferrihydrite.

Under anoxic conditions, the interactions between As-bearing ferrihydrite (Fh) and As(V)-reducing bacteria are known to cause Fh transformations and As mobilization. However, the impact of different types of organic matter (OM) on microbial As/Fe transformation in As-bearing Fh-organic associations remains unclear. In our study, we therefore exposed arsenate-adsorbed ferrihydrite, ferrihydrite-PGA (polygalacturonic acid), and ferrihydrite-HA (humic acid) complexes to two typical Fe(III)- and As(V)-reducing bacteria, and followed the fate of Fe and As in the solid and aqueous phases. Results show that PGA and HA promoted the reductive dissolution of Fh, resulting in 0.7-1.6 and 0.8-1.9 times more As release than in the OM-free Fh, respectively. This was achieved by higher cell numbers in the presence of PGA, and through Fe-reduction via electron-shuttling facilitated by HA. Arsenic-XAS results showed that the solid-phase arsenite fraction in Fh-PGA and Fh-HA was 15-19% and 27-28% higher than in pure Fh, respectively. The solid-associated arsenite fraction likely increased because PGA promoted cell growth and As(V) reduction, while HA provided electron shuttling compounds for direct microbial As(V)-reduction. Collectively, our findings demonstrate that As speciation and partitioning during microbial reduction of Fh-organic associations are strongly influenced by PGA and HA, as well as the strains' abilities to utilize electron-shuttling compounds.

Effects of a Buried Cysteine-To-Serine Mutation on Yeast Triosephosphate Isomerase Structure and Stability

All the members of the triosephosphate isomerase (TIM) family possess a cystein residue (Cys126) located near the catalytically essential Glu165. The evolutionarily conserved Cys126, however, does not seem to play a significant role in the catalytic activity. On the other hand, substitution of this residue by other amino acid residues destabilizes the dimeric enzyme, especially when Cys is replaced by Ser. In trying to assess the origin of this destabilization we have determined the crystal structure of Saccharomyces cerevisiae TIM (ScTIM) at 1.86 Å resolution in the presence of PGA, which is only bound to one subunit. Comparisons of the wild type and mutant structures reveal that a change in the orientation of the Ser hydroxyl group, with respect to the Cys sulfhydryl group, leads to penetration of water molecules and apparent destabilization of residues 132–138. The latter results were confirmed by means of Molecular Dynamics, which showed that this region, in the mutated enzyme, collapses at about 70 ns.

Antimycobacterial and Synergistic Effects of 18β‐Glycyrrhetinic Acid or Glycyrrhetinic acid‐30‐piperazine in Combination with Isoniazid, Rifampicin or Streptomycin against Mycobacterium bovis

18ß-Glycyrrhetinic acid (18ßGA) is a major bioactive component of liquorice with known activity. In this study, we found that both 18ßGA and its derivative glycyrrhetinic acid-30-piperazine (PGA), have potent antimycobacterial properties against the drug-susceptible and drug-resistant Mycobacterium bovis. More importantly, they exhibited synergistic effects with the first-line drugs isoniazid (INH), rifampicin (RIF) and streptomycin (SM) against clinical M. bovis isolates, including drug-resistant strains. In combination with a subinhibitory concentration of 18ßGA, the minimum inhibitory concentrations (MICs) of the anti-tuberculosis agents decreased, ranging from 4- to 16-, 4- to 8- and 4- to 8-fold for INH (fractional inhibitory concentration index (FICI) 0.125-0.375), RIF (FICI 0.118-0.281) and SM (FICI 0.094-0.275), respectively. In the presence of PGA, MICs for the first-line agents resulted in a 4-16-fold decrease for INH (FICI 0.094-0.266, RIF (FICI 0.114-0.313) and SM (FICI 0.094-0.281). Additionally, the MICs of 18ßGA or PGA alone showed significant decreases ranging from 8- to 16-, 8- to 64- and 8- to 128-fold in the presence of INH, RIF and SM, respectively. These findings indicate that 18ßGA and its derivatives might serve as potential therapeutic compounds for future antimycobacterial drug development.

(335) Purification and Characterization of ADP-glucose Pyrophosphorylase from Apple Leaves

Apple leaf ADP-glucose pyrophosphorylase was purified over 1400-fold to apparent homogeneity with a specific activity of 58.9 units per mg of protein. The enzyme was activated by 3-phosphoglycerate (PGA) and inhibited by inorganic phosphate (Pi) in the ADPG synthesis direction. In the pyrophosphorolysis direction, however, high concentrations of PGA (>2.5 mm) inhibited the enzyme activity. The enzyme was resistant to thermal inactivation with a T0.5 (temperature at which 50% of the enzyme activity is lost after 5 min of incubation) of 52 °C. Incubation with 2 mm PGA or 2 mm Pi increased T0.5 to 68 °C. Incubation with 2 mm dithiothreitol (DTT) decreased T0.5 to 42 °C, whereas inclusion of 2 mm PGA in the DTT incubation maintained T0.5 at 52 °C. DTT-induced decrease in thermal stability was accompanied by monomerization of the small subunits. Presence of PGA in the DTT incubation did not alter the monomerization of the small subunits of the enzyme induced by DTT. These findings indicate that the binding of PGA may have dual functions in regulating apple leaf AGPase activity—activating the enzyme and rendering the enzyme with a conformation more stable to thermal inactivation.

Binding of 3-phosphoglycerate leads to both activation and stabilisation of ADP-glucose pyrophosphorylase from apple leaves.

Apple leaf ADP-glucose pyrophosphorylase was purified 1436-fold to apparent homogeneity with a specific activity of 58.9 units mg-1. The enzyme was activated by 3-phosphoglycerate (PGA) and inhibited by inorganic phosphate (Pi) in the ADPG synthesis direction. In the pyrophosphorolytic direction, however, high concentrations of PGA (> 2.5 mm) inhibited the enzyme activity. The enzyme was resistant to thermal inactivation with a T0.5 (temperature at which 50% of the enzyme activity is lost after 5 min incubation) of 52°C. Incubation with 2 mm PGA or 2 mm Pi increased T0.5 to 68°C. Incubation with 2 mm dithiothreitol (DTT) decreased T0.5 to 42°C, whereas inclusion of 2 mm PGA in the DTT incubation maintained T0.5 at 52°C. DTT-induced decrease in thermal stability was accompanied by monomerisation of the small subunits. Presence of PGA in the DTT incubation did not alter the monomerisation of the small subunits of the enzyme induced by DTT. These findings indicate that binding of PGA renders apple leaf AGPase with a conformation that is not only more efficient in catalysis but also more stable to heat treatment. The physiological significance of the protective effect of PGA on thermal inactivation of AGPase is discussed.

Inhibitory effect of L-pyroglutamate on extremophiles: correlation with growth temperature and pH

L-Pyroglutamate (PGA) is naturally occurring from L-glutamate solution with accelerated formation rate under high temperature and low pH. Even though PGA has been identified as a neurotoxic agent on brain cells, the effect of PGA on the growth of microorganisms is rarely known. Here various kinds of microorganisms differing in their optimal growth temperature, pH, phylogeny, and isolated biotope were investigated for the effect of PGA. We found that growth of thermoacidophiles, including both archaea and bacteria, was seriously inhibited by the presence of PGA, and the extent of the inhibitory effect was closely related with growth temperature and pH. Interestingly, only microbes that grow at high temperature and low pH are inhibited by PGA, while this compound may stimulate growth rates of organisms that live at neutral pH and low temperature.

L-pyroglutamic acid inhibits energy production and lipid synthesis in cerebral cortex of young rats in vitro.

In the present study we investigated the effects of L-pyroglutamic acid (PGA), which predominantly accumulates in the inherited metabolic diseases glutathione synthetase deficiency (GSD) and gamma-glutamylcysteine synthetase deficiency (GCSD), on some in vitro parameters of energy metabolism and lipid biosynthesis. We evaluated the rates of CO2 production and lipid synthesis from [U-14C]acetate, as well as ATP levels and the activities of creatine kinase and of the respiratory chain complexes I-IV in cerebral cortex of young rats in the presence of PGA at final concentrations ranging from 0.5 to 3 mM. PGA significantly reduced brain CO2 production by 50% at the concentrations of 0.5 to 3 mM, lipid biosynthesis by 20% at concentrations of 0.5 to 3 mM and ATP levels by 52% at the concentration of 3 mM. Regarding the enzyme activities, PGA significantly decreased NADH:cytochrome c oxireductase (complex I plus CoQ plus complex III) by 40% at concentrations of 0.5-3.0 mM and cytochrome c oxidase activity by 22-30% at the concentration of 3.0 mM, without affecting the activities of succinate dehydrogenase, succinate:DCPIP oxireductase (complex II), succinate:cytochrome c oxireductase (complex II plus CoQ plus complex III) or creatine kinase. The results strongly indicate that PGA impairs brain energy production. If these effects also occur in humans, it is possible that they may contribute to the neuropathology of patients affected by these diseases.

Prostaglandin A 1 enhances c- fos expression and activating protein-1 activity

Prostaglandin A 1 (PGA 1) increases heat shock element (HSE)-mediated transcription, thereby enhancing expression of HSE-bearing genes, including heat shock proteins. Because we recently found functional HSEs in the human and rodent c- fos promoters, we hypothesized that PGA 1 might increase c- fos expression through the HSE. In this study, we revealed that PGA 1 induces c- fos expression at least partly by increasing the binding between heat shock factor-1 and the HSE, and that PGA 1 enhances activity of activating protein-1 (AP-1). Interestingly, so far as PGA 1 is present in the medium, AP-1-mediated transcription enhanced by PGA 1 cannot be detected by the standard luciferase reporter gene assay. Instead, it can be detected by either checking luciferase mRNA levels in the presence of PGA 1 or measuring luciferase activities just after removal of PGA 1. These results showed that protein products of some stress-responsive genes can increase, not during the stressful condition, but immediately after recovery from stress.

Local lattice distortion relating to phosphorus antisite defect in phosphorus-ion-implanted GaP layer

The local lattice distortion relating to the phosphorus antisite defect (PGa) in the P+-ion-implanted GaP layer was studied using Rutherford backscattering (RBS), photoacoustic (PA), Raman scattering, and photoluminescence (PL) methods. The displacement fraction due to the excess phosphorus in 800 °C annealed samples is estimated to be ∼2×1020/cm3 by RBS channeling measurements. The slight reduction of the LO-TO phonon frequency splitting of the annealed P+-ion-implanted GaP with respect to the unimplanted one indicates the presence of PGa, corresponding to x=0.0084 of Ga1−xP1+x. This is consistent with the displacement fraction estimated by RBS. A PL emission relating to PGa is observed at 716 mm (1.73 eV).

Permeabilization of the Plasma Membrane and Maintenance of the Integrity of Organelles in Higher Plant Cells

Plasma membranes of cells isolated from higher plant were permeabilized by a combination of plasmolysis and deplasmolysis in the presence of EGTA. Permeabilized cells, with intact vacuoles, could be separated from intact cells by density gradient centrifugation. The evolution of oxygen in permeabilized cells was measured in the presence of PGA.

Induction of γ-glutamylcysteine synthetase by prostaglandin A2 in L-1210 cells

Effects of prostaglandin A 2 (PGA 2) on glutathione (GSH) status in L-1210 cells were examined. When the cells were cultured in the presence of PGA 2, a persistent rise of cellular GSH concentration was observed 6 h after the addition of PGA 2. This stimulatory effect of PGA 2 was abolished if the cells were pretreated with an enzyme inhibitor of GSH synthesis, buthionine sulfoximine. Subsequent study with cell free extract of cultured L-1210 has revealed that PGA 2 stimulated the biosynthesis of γ-glutamylcysteine synthetase (EC 6.3.2.2). Actinomycin D inhibited this stimulatory effect of PGA 2 on cultured cells. The optimal pH, Km value for glutamic acid and sensitivity to inhibitors of γ-glutamylcysteine synthetase from PGA 2 treated and nontreated cells were virtually the same. Thus, our findings suggest that PGA 2 induced γ-glutamylcysteine synthetase in cultured L-1210 cells which is responsible for the elevated level of GSH in these cells.

Relationship between hormonal, GTP and Ins(1,4,5)P3-stimulated Ca2+ uptake and release in pancreatic acinar cells.

Electrically permeabilized rat pancreatic acini were used to evaluate the contributions of GTP and Ins(1,4,5) P3 to hormone-stimulated Ca2+ uptake and release from intracellular pools. Treatment of permeabilized acini with Ca2+-mobilizing hormones, GTP or GTP[S] resulted in stimulation of an ATP-dependent, VO4(2-)-sensitive Ca2+ uptake into a non-mitochondrial intracellular pool. GTP and GTP[S] also augmented the hormone-mediated stimulation of Ca2+ uptake. Including oxalate in the uptake medium increased Ca2+ uptake into this pool but did not modify the stimulation of Ca2+ uptake induced by hormones or GTP. Ins(1,4,5)P3 released all the extra Ca2+ accumulated as a result of hormone, GTP or GTP[S] stimulation. Hence, these stimuli activated the Ca2+ pump localized in the membrane of the hormone and Ins(1,4,5)P3-sensitive Ca2+ pool. Including 2,3-diphosphoglyceric acid (PGA) [an inhibitor of Ins(1,4,5)P3 hydrolysis] in the incubation medium blunted the GTP and GTP[S]-stimulated Ca2+ uptake. In the presence of PGA, the hormones inhibited Ca2+ accumulation, and GTP and GTP[S] augmented this effect. Accordingly, PGA stabilized the Ins(1,4,5)P3-evoked Ca2+ release from intracellular pools. Only in the presence of PGA was it possible to demonstrate hormonally-evoked Ca2+ release from permeabilized cells. GTP, and more importantly GTP[S], augmented the hormone-evoked Ca2+ release. Hormones and Ins(1,4,5)P3 in the presence or absence of GTP or GTP[S] released Ca2+ from the same intracellular pool. The extent of Ca2+ release caused by the combination of hormones and GTP or GTP[S] was similar to that evoked by Ins(1,4,5)P3 alone. Taken together, these results suggest that GTP or GTP[S] facilitates stimulation of phospholipase C by hormones. Such stimulation results in stimulation of protein kinase C and increased levels of Ins(1,4,5)P3 and is sufficient to explain the effects of GTP and GTP[S] on Ca2+ uptake and release from pancreatic acinar cells.

Effect of poly(α-D-glutamic acid) on the polarographic reduction of 3,6-diaminoacridines

The effect of poly(α-D-glutamic acid) (PGA) on the Tast polarographic reduction of trypaflavine (TrFl) as a representative of the 3,6-diaminoacridines was studied. In the polarograms of 0.1 m M TrFl, two reduction waves were observed. The first wave corresponded to the formation of a TrFl radical. In the presence of PGA in acid solutions, the half-wave potential of the first wave of TrFl shifted towards negative values, while the limiting current decreased. The absorption spectra and drop time curves for the TrFl solution with and without PGA were also examined. It is concluded that the TrFl molecule is bound to a PGA molecule in the bulk to form a complex. At appropriate concentrations of the complex, an adsorption layer was formed on the electrode. The second wave corresponds to the formation of acridan by one-electron reduction accompanied by protonation. Upon addition of PGA to the solution, the half-wave potential of this wave shifted remarkably towards positive values with the PGA concentration, although a considerable decrease was observed in the limiting current. This behaviour was pronounced in the pH region where the PGA-H + chelate complex is formed. It is deduced that in the electroreduction of TrFl in the second step, the H + ion is supplied mainly from the PGA-H + complex, which is present in close proximity to the TrFl radical on the electrode.

Inhibited light activation of fructose and sedoheptulose bisphosphatase in spinach chloroplasts exposed to osmotic stress

The light activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) and sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) was inhibited in isolated intact spinach (Spinacia oleracea L.) chloroplasts exposed to reduced osmotic potentials. Decreases in the velocity and magnitude of light activation correlated with the overall reduction in CO2 fixation rates. Responses of osmotically stressed chloroplasts to both varying pH and exogeous dihydroxyacetone phosphate (DHAP) or 3-phosphoglycerete (PGA) were examined. In the presence of DHAP, the absolute rate of CO2 fixation was increased and this increase was most pronounced at alkaline pH. Enhanced light activation of these enzymes was also observed under these conditions. However, in the presence of PGA, similar increases in photosynthetic rate and enzyme activation were not evident. Light-dependent stromal alkalization was unaffected by the stress treatments. Inhibition of light activation under hypertonic conditions is discussed in terms of substrate availability, possible alterations of the redox state of ferredoxin and associated electron carriers, and inhibited enzyme-enzyme or enzyme-substrate interactions involved in the light activation process.

Autocatalysis and light activation of enzymes in relation to photosynthetic induction in wheat chloroplasts

In order to study the relative contributions of the autocatalytic increase in the level of substrates and the light activation of enzymes to the control of the induction phase or “lag” in wheat chloroplasts, we measured the light-induced reductive activation of fructose 1,6-bisphosphatase, phosphoglycerate kinase, NADP +-dependent glyceraldehyde-phosphate dehydrogenase, ribulose 1,5-bisphosphate carboxylase, and phosphoribulokinase in isolated chloroplasts. Each was rapidly activated to levels more than adequate to support the maximum rate of photosynthesis. Induction in wheat chloroplasts is characterized by a period of about 1 min during which no O 2 is evolved. If small quantities of intermediates such as dihydroxyacetone phosphate (DHAP) or 3-phosphoglycerate (PGA) are added, maximum rates of photosynthesis are achieved within the first minute of illumination. The presence of PGA did not affect the activation of any of the above-mentioned enzymes. Each of the enzymes was therefore capable of sustaining maximum rates of photosynthesis in the presence of PGA, even though there was no O 2 evolution from those chloroplasts incubated with CO 2 alone as substrate. The inclusion of PGA did not give rise to abnormally high levels of DHAP, FBP, or fructose 6-phosphate in the stroma. We conclude that the levels of substrates or cofactors are the principal, if not the sole, determinants of the rate of photosynthetic carbon assimilation during induction in wheat chloroplasts.