Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00790 (PGA)
 2,475 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

ADP-glucose (Glc) pyrophosphorylase (AGPase), a key regulatory enzyme in starch biosynthesis, is highly regulated. Transgenic approaches in four plant species showed that alterations in either thermal stability or allosteric modulation increase starch synthesis. Here, we show that the classic regulators 3-phosphoglyceric acid (3-PGA) and inorganic phosphate (Pi) stabilize maize (Zea mays) endosperm AGPase to thermal inactivation. In addition, we show that glycerol phosphate and ribose-5-P increase the catalytic activity of maize AGPase to the same extent as the activator 3-PGA, albeit with higher K(a) (activation constant) values. Activation by fructose-6-P and Glc-6-P is comparable to that of 3-PGA. The reactants ATP and ADP-Glc, but not Glc-1-P and pyrophosphate, protect AGPase from thermal inactivation, a result consistent with the ordered kinetic mechanism reported for other AGPases. 3-PGA acts synergistically with both ATP and ADP-Glc in heat protection, decreasing the substrate concentration needed for protection and increasing the extent of protection. Characterization of a series of activators and inhibitors suggests that they all bind at the same site or at mutually exclusive sites. Pi, the classic "inhibitor" of AGPase, binds to the enzyme in the absence of other metabolites, as determined by thermal protections experiments, but does not inhibit activity. Rather, Pi acts by displacing bound activators and returning the enzyme to its activity in their absence. Finally, we show from thermal inactivation studies that the enzyme exists in two forms that have significantly different stabilities and do not interconvert rapidly.
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PMID:Heat stability and allosteric properties of the maize endosperm ADP-glucose pyrophosphorylase are intimately intertwined. 1802 61

We have previously demonstrated the ability of poly(glycerol adipate) backbone (PGA) and PGA polymer backbone substituted with varying amounts of pendant C(18) chain length acyl groups to yield Dexamethasone phosphate DXMP loaded nanoparticles. The aim of this study was to obtain a deeper understanding of the underlying principles responsible for good drug incorporation and controlled release of drugs from poly (glycerol adipate) (PGA) nanoparticles. We compared the incorporation of the water soluble drugs DXMP and Cytosine arabinoside (CYT-ARA) in both unmodified and substituted PGA polymers. We investigated the effect of change in acyl group chain length and the degree of substitution on the physicochemical properties, drug loading and release of DXMP and CYT-ARA. Nanoparticles were prepared by the interfacial deposition technique and the simultaneous emulsification method. Amongst the nanoparticles prepared using acylated polymers with varying chain lengths (C(2) to C(10)) for DXMP incorporation, polymers with acyl group chain lengths containing 8 carbon atoms (C(8)) showed maximum drug incorporation. Amongst the C(8) series, polymers with 100% acylation provided both good drug incorporation and a controlled release for DXMP while for CYT-ARA it was the unsubstituted polymer backbone that had maximum drug loading and slower release. A number of inter-related factors are responsible for producing particles with particular size, zeta potential, drug loading and release characteristics. Drug loading and release from nanoparticles are primarily influenced by the nature of interactions between the drug and polymers which in turn depend upon the type of drug used and the physical chemistry of the polymer.
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PMID:Drug incorporation and release of water soluble drugs from novel functionalized poly(glycerol adipate) nanoparticles. 1803 43

Polymer-based microparticles are increasingly becoming of interest for a variety of applications including drug delivery. Recently poly(glycerol adipate) (PGA) and poly(glycol adipate-co-omega-pentadecalactone) have shown promise for delivery of dexamethasone phosphate and ibuprofen. In this paper the copolyester poly(glycol adipate-co-omega-pentadecalactone) was evaluated as a colloidal delivery system for encapsulated therapeutic proteins. Enzyme containing microparticles were prepared via the double water-in-oil-in-water (w/o/w) emulsion-solvent evaporation methodology. alpha-Chymotrypsin was used as a model proteolytic enzyme and its transfer was monitored during the emulsification process, in addition to in vitro release from formed particles. On average, 22.1 microg protein per 1 mg polymer was encapsulated, although gradual loss of activity of the protein, once released, was recorded. The work presented shows the potential of this polyester as a delivery system for enzymes via microparticles, with improvements to the system achievable via polymer and process optimization. The pendant hydroxyl groups on the polymer backbone provide future capacity for tailored alteration of the physical and chemical properties of the polymer, in addition to covalent attachment of various compounds.
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PMID:Encapsulation and release of alpha-chymotrypsin from poly(glycerol adipate-co-omega-pentadecalactone) microparticles. 1838 25

ADP-glucose pyrophosphorylase (AGPase) catalyzes the rate-limiting step in starch biosynthesis in plants and changes in its catalytic and/or allosteric properties can lead to increased starch production. Recently, a maize (Zea mays)/potato (Solanum tuberosum) small subunit mosaic, MP [Mos(1-198)], containing the first 198 amino acids of the small subunit of the maize endosperm enzyme and the last 277 amino acids from the potato tuber enzyme, was expressed with the maize endosperm large subunit and was reported to have favorable kinetic and allosteric properties. Here, we show that this mosaic, in the absence of activator, performs like a wild-type AGPase that is partially activated with 3-phosphoglyceric acid (3-PGA). In the presence of 3-PGA, enzyme properties of Mos(1-198)/SH2 are quite similar to those of the wild-type maize enzyme. In the absence of 3-PGA, however, the mosaic enzyme exhibits greater activity, higher affinity for the substrates, and partial inactivation by inorganic phosphate. The Mos(1-198)/SH2 enzyme is also more stable to heat inactivation. The different properties of this protein were mapped using various mosaics containing smaller portions of the potato small subunit. Enhanced heat stability of Mos(1-198) was shown to originate from five potato-derived amino acids between 322 and 377. These amino acids were shown previously to be important in small subunit/large subunit interactions. These five potato-derived amino acids plus other potato-derived amino acids distributed throughout the carboxyl-terminal portion of the protein are required for the enhanced catalytic and allosteric properties exhibited by Mos(1-198)/SH2.
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PMID:Characterization of an autonomously activated plant ADP-glucose pyrophosphorylase. 1871 54

Pepsin partitioning, a gastric acid protease, in aqueous two-phase systems of polyethyleneglycol/potassium phosphate, sodium citrate and ammonium sulphate was assayed using polyethylenglycol of different molecular mass. Pepsin was found to be partitioned towards the polymer-rich phase in all the systems, which suggests an important protein-polymer interaction due to the highly hydrophobic character of the protein surface exposed to the solvent. The pepsin partitioning behavior was explained according to Timasheff's preferential interaction theory. The process was driven entropically with participation of structured water around the polyethyleneglycol ethylenic chains. The best pepsin recovery was observed in the systems polyethyleneglycol molecular mass 600. These systems were chosen in order to assay the bovine stomach homogenate partition and to compare different working conditions such as the top-bottom phase volume ratio and homogenate proportions in the total system. The best purification factors were obtained with PEG600/potassium phosphate with low top-bottom volume ratio using 15% of bovine stomach homogenate in the system total mass.
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PMID:Pepsin extraction from bovine stomach using aqueous two-phase systems: molecular mechanism and influence of homogenate mass and phase volume ratio. 1877 46

Methylglyoxal (MG) was studied as an inhibitor and effective glycating factor of human muscle-specific enolase. The inhibition was carried out by the use of a preincubation procedure in the absence of substrate. Experiments were performed in anionic and cationic buffers and showed that inhibition of enolase by methylglyoxal and formation of enolase-derived glycation products arose more effectively in slight alkaline conditions and in the presence of inorganic phosphate. Incubation of 15 micromolar solutions of the enzyme with 2 mM, 3.1 mM and 4.34 mM MG in 100 mM phosphate buffer pH 7.4 for 3 h caused the loss a 32%, 55% and 82% of initial specific activity, respectively. The effect of MG on catalytic properties of enolase was investigated. The enzyme changed the K(M) value for glycolytic substrate 2-phospho-D-glycerate (2-PGA) from 0.2 mM for native enzyme to 0.66 mM in the presence of MG. The affinity of enolase for gluconeogenic substrate phosphoenolpyruvate altered after preincubation with MG in the same manner, but less intensively. MG has no effect on V(max) and optimal pH values. Incubation of enolase with MG for 0-48 h generated high molecular weight protein derivatives. Advanced glycation end products (AGEs) were resistant to proteolytic degradation by trypsin. Magnesium ions enhanced the enzyme inactivation by MG and facilitated AGEs formation. However, the protection for this inhibition in the presence of 2-PGA as glycolytic substrate was observed and AGEs were less effectively formed under these conditions.
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PMID:Inhibition of human muscle-specific enolase by methylglyoxal and irreversible formation of advanced glycation end products. 1883 Aug 74

Wound infection is a complication feared in surgery. The aim of this study was to develop new anti-infective coatings of surgical sutures and to compare the anti-microbial effectiveness and biocompatibility to the well-established Vicryl Plus. Synthetic absorbable PGA surgical sutures were coated with three different chlorhexidine concentrations and two different octenidine concentrations in combination with palmitic acid and lauric acid. Drug-release kinetics lasting 96 h were studied in phosphate-buffered saline at 37 degrees C. Anti-infective characteristics were determined by measuring the change in optical density of Staphylococcus aureus suspensions charged with coated sutures over time. Microorganisms adsorbed at the surface of coated sutures were assessed on blood agar plates and coated sutures eluted for 24 h were placed on bacterial lawns cultured on Mueller-Hinton plates to prove retained anti-microbial potency. A cell proliferation assay was performed to assess the degree of cytotoxicity. Anti-infective characteristics and biocompatibility were compared to Vicryl Plus. A coating technology for slow-release drug-delivery systems on surgical sutures could be developed. All coatings showed a continuous drug release within 96 h. Individual chlorhexidine and octenidine coated sutures showed superior anti-infective characteristics but inferior biocompatibility in comparison to Vicryl Plus. We conclude that the developed anti-infective suture coatings consisting of lipid-based drug-delivery systems in combination with antiseptics are highly effective against bacterial colonization in vitro; however, drug doses have to be adjusted to improve biocompatibility.
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PMID:New anti-infective coatings of surgical sutures based on a combination of antiseptics and fatty acids. 1962 81

Maize (Zea mays) endosperm ADP-glucose pyrophosphorylase (AGPase) is a highly regulated enzyme that catalyzes the rate-limiting step in starch biosynthesis. Although the structure of the heterotetrameric maize endosperm AGPase remains unsolved, structures of a nonnative, low-activity form of the potato tuber (Solanum tuberosum) AGPase (small subunit homotetramer) reported previously by others revealed that several sulfate ions bind to each enzyme. These sites are also believed to interact with allosteric regulators such as inorganic phosphate and 3-phosphoglycerate (3-PGA). Several arginine (Arg) side chains contact the bound sulfate ions in the potato structure and likely play important roles in allosteric effector binding. Alanine-scanning mutagenesis was applied to the corresponding Arg residues in both the small and large subunits of maize endosperm AGPase to determine their roles in allosteric regulation and thermal stability. Steady-state kinetic and regulatory parameters were measured for each mutant. All of the Arg mutants examined--in both the small and large subunits--bound 3-PGA more weakly than the wild type (A(50) increased by 3.5- to 20-fold). By contrast, the binding of two other maize AGPase allosteric activators (fructose-6-phosphate and glucose-6-phosphate) did not always mimic the changes observed for 3-PGA. In fact, compared to 3-PGA, fructose-6-phosphate is a more efficient activator in two of the Arg mutants. Phosphate binding was also affected by Arg substitutions. The combined data support a model for the binding interactions associated with 3-PGA in which allosteric activators and inorganic phosphate compete directly.
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PMID:Probing allosteric binding sites of the maize endosperm ADP-glucose pyrophosphorylase. 1988 75

We report the design and preparation of polyion complex (PIC) nanoparticles composed of anionic hydrophobically modified and cationic poly(amino acid) and the effect of hydrophobic interactions on the stability of these PIC nanoparticles under physiological conditions. We selected poly(gamma-glutamic acid) (gamma-PGA) as the biodegradable anionic polymer and poly(epsilon-lysine) (epsilon-PL) as the cationic polymer. Amphiphilic graft copolymers consisting of gamma-PGA and L-phenylalanine (L-Phe) as the hydrophobic side chain were synthesized by grafting L-Phe to gamma-PGA. The PIC nanoparticles were prepared by mixing gamma-PGA-graft-L-Phe (gamma-PGA-Phe) with epsilon-PL in phosphate buffered saline (PBS). The formation and stability of the PIC nanoparticles were investigated by dynamic light scattering (DLS) measurements. Monomodal anionic PIC nanoparticles were obtained using nonstoichiometric mixing ratios. When unmodified gamma-PGA was mixed with epsilon-PL in PBS, the formation of PIC nanoparticles was observed. However, within a few hours after the preparation, the PIC nanoparticles dissolved in the PBS. In contrast, gamma-PGA-Phe/epsilon-PL nanoparticles showed high stability for a prolonged period of time in PBS and over a wide range of pH values. The stability and size of the PIC nanoparticles depended on the gamma-PGA-Phe/epsilon-PL mixing ratio and the hydrophobicity of the gamma-PGA. The improved stability of the PIC nanoparticles was attributed to the formation of hydrophobic domains in the core of the nanoparticles. The fabrication of PIC nanoparticles using hydrophobic interactions was very useful for the stabilization of the nanoparticles. These results will provide a novel concept in the design of carrier systems composed of PIC. It is expected that the gamma-PGA-Phe/epsilon-PL nanoparticles will have great potential as multifunctional carriers for pharmaceutical and biomedical applications, such as drug and vaccine delivery systems.
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PMID:Stabilization of polyion complex nanoparticles composed of poly(amino acid) using hydrophobic interactions. 2001 13

ADP-glucose pyrophosphorylase catalyzes the synthesis of ADP-glucose (ADP-Glc) from Glc-1-phosphate (G-1-P) and ATP. Kinetic studies were performed to define the nature of the reaction, both in the presence and absence of allosteric effector molecules. When 3-phosphoglycerate (3-PGA), the putative physiological activator, was present at a saturating level, initial velocity studies were consistent with a Theorell-Chance BiBi mechanism and product inhibition data supported sequential binding of ATP and G-1-P, followed by ordered release of pyrophosphate and ADP-Glc. A sequential mechanism was also followed when 3-PGA was absent, but product inhibition patterns changed dramatically. In the presence of 3-PGA, ADP-Glc is a competitive inhibitor with respect to ATP. In the absence of 3-PGA--with or without 5.0 mm inorganic phosphate--ADP-Glc actually stimulated catalytic activity, acting as a feedback product activator. By contrast, the other product, pyrophosphate, is a potent inhibitor in the absence of 3-PGA. In the presence of subsaturating levels of allosteric effectors, G-1-P serves not only as a substrate but also as an activator. Finally, in the absence of 3-PGA, inorganic phosphate, a classic inhibitor or antiactivator of the enzyme, stimulates enzyme activity at low substrate by lowering the K(M) values for both substrates.
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PMID:Studies of the kinetic mechanism of maize endosperm ADP-glucose pyrophosphorylase uncovered complex regulatory properties. 2001


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