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)

Absorbable fibers of linear poly-alpha-hydroxy acids have been used successfully in providing temporary scaffolds for tissue regeneration. In some surgical applications, degradation rates for poly(glycolide) (PGA) are too high, but implants of poly(L-lactide) (PLLA) fibers may degrade too slowly for optimal function. Polymers produced by copolymerization of L-lactide with varying amounts of D-lactide may offer an alternative choice for absorbable fiber based implants. Poly(L/D-lactide) stereocopolymers with L/D lactide molar ratios of 95/5, 90/10, and 85/15 were considered. Melt-spun/hot-drawn fibers with L/D molar ratios of 90/10 and 85/15 and draw ratios ranging from 3.0 to 8.9 were further evaluated by mechanical testing, differential scanning calorimetry, birefringence, x-ray diffraction, and in vitro exposure to pH 7.4 phosphate buffered saline at 37 degrees C. Fabrication was reproducible and results indicated that tensile strength, modulus, an birefringence all increased with increasing draw ratio up to a draw ratio of 6.7 and declined thereafter; elongation to failure decreased for the entire range studied. For fibers with a draw ratio of 6.7, there was a 10% relative difference in crystallinity between the 90/10 and 85/15 lactide fibers (90/10 was higher). Wet strength retention after 12 weeks in vitro exposure was approximately 10% for the 90/10 fibers and 30% for the 85/15 fibers. The intermediate wet strength retention of lactide stereocopolymer fibers when compared to reported values for PGA and PLLA fibers, suggests these materials may be useful in absorbable surgical implants for tissue repair and regeneration.
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PMID:Processing and characterization of absorbable polylactide polymers for use in surgical implants. 1017 72

Nonphosphorylating glyceraldehyde 3-phosphate dehydrogenase (GAPN) from Streptococcus mutans which catalyzes the irreversible oxidation of D-glyceraldehyde-3 phosphate (D-G3P) into 3-phosphoglycerate (3-PGA) in the presence of NADP belongs to the aldehyde dehydrogenase (ALDH) superfamily. Oxidation of D-G3P into 3-PGA by GAPN involves the formation of a covalent enzyme intermediate via the nucleophilic attack of the invariant Cys-302. Titration of Cys-302 in the apo-enzyme by two different kinetic probes, iodoacetamide and 2,2'-dipyridyl disulfide, shows a pK(app) of 8.5 and a chemical reactivity surprisingly low compared to a reactive and accessible thiolate. Binding of NADP causes a strong increase of the reactivity of Cys-302-which is time dependent-with a pK(app) shift from 8.5 to 6.1. Concomitant with the increase in the Cys-302 reactivity, an additional protein fluorescence quenching is observed. These data suggest that cofactor binding induces at least a local conformational rearrangement within the active site. The efficiency of the rearrangement depends on the structure of the cofactors and on the protonation of an amino acid with a pK(app)( )()of 5.7. The rate of the rearrangement also strongly increases when temperature decreases. The data on the conformational rearrangement also reveal an amino acid with a pK(app) of 7.6 whose deprotonation increases the reactivity of the thiolate of Cys-302 by a 3-fold factor. The nature of the amino acid involved-which should be located close to Cys-302 in the holo-active form-is likely the invariant Glu-268. Changing Glu-268 into Ala or Cys-302 into Ala leads to mutants in which the rearrangement is only efficient in the presence of saturating concentrations of both NADP and G3P. The structural aspects of the conformational rearrangement occurring during the catalytic process in the wild-type GAPN should include at least reorientation of both Cys-302 and Glu-268 side chains and repositioning of the nicotinamide ring of the cofactor to permit the chemical activation of Cys-302 and the formation of an efficient ternary complex. Thus, it is likely that the conformation of the active site in the reported X-ray structures of ALDHs determined so far in the presence of cofactor, in which the side chains of Cys-302 and Glu-268 are 6.7 A apart from each other, does not represent the biological active form.
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PMID:Evidence for the chemical activation of essential cys-302 upon cofactor binding to nonphosphorylating glyceraldehyde 3-phosphate dehydrogenase from Streptococcus mutans. 1050 67

Photosynthetic carbon metabolism was investigated in antisense Arabidopsis lines with decreased expression of sucrose phosphate synthase (SPS) and cytosolic fructose-1,6-bisphosphatase (cFBPase). In the light, triose phosphates are exported from the chloroplast and converted to sucrose via cFBPase and SPS. At night, starch is degraded to glucose, exported and converted to sucrose via SPS. cFBPase therefore lies upstream and SPS downstream of the point at which the pathways for sucrose synthesis in the day and night converge. Decreased cFBPase expression led to inhibition of sucrose synthesis; accumulation of phosphorylated intermediates; Pi-limitation of photosynthesis; and stimulation of starch synthesis. The starch was degraded to maintain higher levels of sugars and a higher rate of sucrose export during the night. This resembles the response in other species when expression of enzymes in the upper part of the sucrose biosynthesis pathway is reduced. Decreased expression of SPS inhibited sucrose synthesis, but phosphorylated intermediates did not accumulate and carbon partitioning was not redirected towards starch. Sugar levels and sucrose export was decreased during the night as well as during the day. Although ribulose-1,5-bisphosphate regeneration and photosynthesis were inhibited, the PGA/triose-P ratio remained low and the ATP/ADP ratio high, showing that photosynthesis was not limited by the rate at which Pi was recycled during end-product synthesis. Two novel responses counteracted the decrease in SPS expression and explain why phosphorylated intermediates did not accumulate, and why allocation was not altered in the antisense SPS lines. Firstly, a threefold decrease of PPi and a shift of the UDP-glucose/hexose phosphate ratio favoured sucrose synthesis and prevented the accumulation of phosphorylated intermediates. Secondly, there was no increase of AGPase activity relative to cFBPase activity, which would prevent a shift in carbon allocation towards starch synthesis. These responses are presumably triggered when sucrose synthesis is decreased in the night, as well as by day.
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PMID:Decreased expression of two key enzymes in the sucrose biosynthesis pathway, cytosolic fructose-1,6-bisphosphatase and sucrose phosphate synthase, has remarkably different consequences for photosynthetic carbon metabolism in transgenic Arabidopsis thaliana. 1099 87

We report on the development and characterization of a new composite material consisting of amorphous carbonated apatite, Ca(5)(PO(4), CO(3))(3)(OH), and microstructured poly(hydroxyacetic acid), polyglycolide (PGA). This material is able to keep the pH of a surrounding solution within the physiological range (7.2-7.6). This was achieved by chemical fine-tuning of the counterplay between the acidic degradation of the polyester and the basic dissolution of calcium phosphate. Microporous samples with pore sizes of <1 microm and compact samples were prepared. The biological behavior was assayed in vitro by long-term osteoblast culture. Morphological and biochemical analyses of cell differentiation revealed excellent biocompatibility, leading to cell attachment, collagen and osteocalcin expression, and mineral deposition. This material could be of use as a biodegradable bone substitution material and as a scaffold for tissue engineering.
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PMID:Biologically and chemically optimized composites of carbonated apatite and polyglycolide as bone substitution materials. 1109 75

Cell attachment to a scaffold is a precondition for the development of bioengineered valves and vascular substitutes. This attachment is generally facilitated by the use of precoating factors, but some can cause toxic or immunologic side effects. Autologous extracellular matrix (ECM) is used as a precoating factor in our study. Ascending aortic tissue was cultured to obtain human myofibroblasts. Autologous ECM was extracted from the same aortic tissue. Poly(glycolic acid) (PGA) scaffolds were precoated with autologous ECM, human serum, or poly-L-lysine; the control group was pretreated with phosphate buffered saline (PBS). Myofibroblasts were seeded onto each scaffold, and the cell attachment was assayed and compared. Compared with the control group, precoating with human serum, poly-L-lysine, and ECM increased number of attached cells by 24%, 53%, and 48%, respectively. Differences between precoating groups were significant (p < 0.01), except for ECM versus poly-L-lysine. Scanning electron microscopy also demonstrated the high degree of cell attachment to the PGA fibers on scaffolds precoated with ECM and poly-L-lysine. Precoating polymeric scaffold with autologous human extracellular matrix is a very effective method of improving cell attachment in cardiovascular tissue engineering without the potential risk of immunologic reactions.
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PMID:Scaffold precoating with human autologous extracellular matrix for improved cell attachment in cardiovascular tissue engineering. 1111 Feb 71

We prepared natto (fermented soybeans) mucilage containing poly-gamma-glutamic acid (gamma-PGA) from commercial natto. The effect of natto mucilage on calcium (Ca) solubility in vitro and in vivo was investigated. Ca solubility in vitro increased with an increase in the amount of natto mucilage, due to inhibition of the formation of an insoluble complex of Ca with phosphate by natto mucilage. Rats were fed with 5 g of soybean protein isolate, natto, mucilage-free natto, or natto mucilage diet for 1.5 h. Small intestinal contents were collected 2.5 h after ingestion. In the lower half of the small intestine, both the amount and the percentage of soluble Ca of intestinal contents were significantly higher (P < 0.001) in rats fed with natto mucilage diet than in those fed with the other diets. Natto mucilage also increased Ca solubility in vivo. These results suggested that gamma-PGA is responsible for the increasing effect of natto mucilage on Ca solubility.
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PMID:Natto mucilage containing poly-gamma-glutamic acid increases soluble calcium in the rat small intestine. 1133 Jun 62

Spectroscopic and kinetic methods have been used to explore the roles of divalent metal ions in the enolase-catalyzed dehydration of 2-phosphoglycerate (2-PGA). Enolase requires 2 equiv of metal ion per active site for maximal activity. Previous crystallographic studies [Larsen, T. M., Wedekind, J. E., Rayment, I., and Reed, G. H. (1996) Biochemistry 35, 4349-4358] showed that both magnesium ions coordinated to the carboxylate group of the substrate/product-a scheme consistent with metal ion assistance in formation of the enolate intermediate. Electron paramagnetic resonance (EPR) data with 17O-labeled forms of phosphoenolpyruvate show that Mn(2+), bound at the lower affinity site, coordinates to one carboxylate oxygen and one phosphate oxygen of the substrate. These observations are fully consistent with the crystallographic data. Plots of activity versus log [metal ion] are bell-shaped, and the inhibitory phases of the profiles have been previously attributed to binding of metal ions at ancillary sites on the enzyme. However, the activation profiles and measurements of 2H kinetic isotope effects support an ordered kinetic mechanism wherein binding of 2-PGA precedes binding of the second metal ion, and release of the second metal ion occurs prior to departure of phosphoenolpyruvate. High concentrations of metal ion lead to inhibition in the ordered mechanism by interfering with product release. The 2H kinetic isotope effect is diminished in the inhibitory phases of the metal ion activation profiles in a manner that is consistent with the predominantly ordered mechanism. Zn(2+) gives lower maximal activity than Mg(2+), apparently due to slow release of Zn(2+) from the product complex. Addition of imidazole increases the maximal rate apparently by accelerating the release of Zn(2+) from the enzyme.
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PMID:Role of metal ions in catalysis by enolase: an ordered kinetic mechanism for a single substrate enzyme. 1143 70

The immobilization of Penicillin G Acylase from Bacillus megaterium by glutaraldehyde crosslinking on the partially acid-hydrolyed polyacrylonitrile fiber was studied. When the amount of--NH2 on fiber were 690 mumol/g and the moisture in the fiber was 64%, and the content of enzyme protein immobilized on fiber was more than 100 mg/g. The activity of 2300 IU/g was obtained with 30% of overall yield and 56% of binding efficiency. The immobilization yield was markedly influenced by ratio of the amount of free enzyme used to the weight of the fiber. The half-life of storage stability of immobilized PGA at room temperature was 130 days. The immobilized PGA kept 80% of the initial activity after 20 cycles of operation in 10% of PGK(W/V) in 0.05 mol/L phosphate buffer, pH 8.0, at 37 degrees C and an enzyme load of 150 IU/g(PGK) and 10 g(PGK) for per cycle of operation. The hydrolysis conversion of PGK in the range of 2.5%-12.5% (W/V) were over 98% for the immobilized PGA. The operation stability of immobilized PGA treated with DTT was better than that of immobilized PGA untreated.
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PMID:[Immobilization of penicilin G acylase on polyacrylonitrile fiber]. 1255 15

Escherichia coli 3-deoxy-D-manno-octulosonate 8-phosphate (KDO8-P) synthase is able to utilize the five-carbon phosphorylated monosaccharide, 2-deoxyribose 5-phosphate (2dR5P), as an alternate substrate, but not D-ribose 5-phosphate (R5P) nor the four carbon analogue D-erythrose 4-phosphate (E4P). However, E. coli KDO8-P synthase in the presence of either R5P or E4P catalyzes the rapid consumption of approximately 1 mol of PEP per active site, after which consumption of PEP slows to a negligible but measurable rate. The mechanism of this abortive utilization of PEP was investigated using [2,3-(13)C(2)]-PEP and [3-F]-PEP, and the reaction products were determined by (13)C, (31)P, and (19)F NMR to be pyruvate, phosphate, and 2-phosphoglyceric acid (2-PGA). The formation of pyruvate and 2-PGA suggests that the reaction catalyzed by KDO8-P synthase may be initiated via a nucleophilic attack to PEP by a water molecule. In experiments in which the homologous enzyme, 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAH7-P) synthase was incubated with D,L-glyceraldehyde 3-phosphate (G3P) and [2,3-(13)C(2)]-PEP, pyruvate and phosphate were the predominant species formed, suggesting that the reaction catalyzed by DAH7-P synthase starts with a nucleophilic attack by water onto PEP as observed in E. coli KDO8-P synthase.
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PMID:Mechanistic insight into 3-deoxy-D-manno-octulosonate-8-phosphate synthase and 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase utilizing phosphorylated monosaccharide analogues. 1271 25

1. Pepsinogen B, the precursor of pepsin B, has been isolated by ion-exchange chromatography and gel filtration from neutral extracts of pig gastric mucosa. The material possesses potential activity against acetyl-l-phenylalanyl-l-di-iodotyrosine and against gelatin but has little, if any, potential activity against haemoglobin. 2. The material appears homogeneous in the ultracentrifuge, but on gel filtration and on electrophoresis in starch gel it is shown to be contaminated with a small amount of material having potential activity against haemoglobin. On electrophoresis in starch gel also the material is shown to contain about equal amounts of two major components, both of which have potential activity against the synthetic substrate. Pepsin B has also been shown to contain two active components by electrophoresis under the same conditions. 3. The zymogen is similar to pepsinogen and pepsinogen C in its molecular weight and general physico-chemical properties, but differs from these zymogens in the nature of its N-terminal residues. It is possible that one of the components contains 1 mole of bound phosphate/mole. 4. The material is activated rapidly at pH2 and more slowly at pH4. At both pH values the kinetics of the activation reaction are complex.
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PMID:PEPSINOGEN B: THE ZYMOGEN OF PEPSIN B. 1434 55


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