Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.1.2.13 (aldolase)
3,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The distributions and rates of transfer of carbon isotopes from a selection of specifically labelled ketosugar-phosphate substrates by exchange reactions catalyzed by the pentose and photosynthetic carbon-reduction-pathway group-transferring enzymes transketolase, transaldolase and aldolase have been measured using 13C-NMR spectroscopy. 2. The rates of these exchange reactions were 5, 4 and 1.5 mumol min-1 mg-1 for transketolase exchange, transaldolase exchange and aldolase exchange, respectively. 3. A comparison of the exchange capacities contributed by the activities of these enzymes in three in vitro liver preparations with the maximum non-oxidative pentose pathway flux rates of the preparations shows that transketolase and aldolase exchanges exceeded flux by 9-19 times in liver cytosol and acetone powder enzyme preparations and by 5 times in hepatocytes. Transaldolase was less effective in the comparison of exchange versus flux rates: transaldolase exchange exceeded flux by 1.6 and 5 in catalysis by liver cytosol and acetone powder preparations, respectively, but was only 0.6 times the flux in hepatocytes. 4. Values of group enzyme exchange and pathway flux rates in the above three preparations are important because of the feature role of liver and of these particular preparations in the establishment, elucidation and measurement of a proposed reaction scheme for the fat-cell-type pentose pathway in biochemistry. 5. It is the claim of this paper that the excess of exchange rate activity (particularly transketolase exchange) over pathway flux will overturn attempts to unravel, using isotopically labelled sugar substrates, the identity, reaction sequence and quantitative contribution of the pentose pathway to glucose metabolism. 6. The transketolase exchange reactions relative to the pentose pathway flux rates in normal, regenerating and foetal liver, Morris hepatomas, mammary carcinoma, melanoma, colonic epithelium, spinach chloroplasts and epididymal fat tissue show that transketolase exchange may exceed flux in these tissues by factors ranging over 5-600 times. 7. The confusion of pentose pathway theory by the effects of transketolase exchange action is illustrated by the 13C-NMR spectrum of the hexose 6-phosphate products of ribose 5-phosphate dissimilation, formed after 30 min of liver enzyme action, and shows 13C-labelling in carbons 1 and 3 of glucose 6-phosphate with ratios which range over 2.1-6.4 rather than the mandatory value of 2 which is imposed by the theoretical mechanism of the pathway.
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PMID:Exchange reactions catalyzed by group-transferring enzymes oppose the quantitation and the unravelling of the identify of the pentose pathway. 847 19

The 9-amino or 9-N-acyl-5-trifluoroacetyl methyl alpha-ketosides (1a-c) and their 2,3-didehydro analogs (2a-c) have been synthesized through Neu5Ac aldolase-catalyzed aldol reaction of 6-azido-2-benzyloxycarbonylamino-2-deoxy-D-mannose with sodium pyruvate. The six compounds were investigated as inhibitors of sialidase from influenza virus. Compound 2b, a 2,3-didehydro type, showed the most potent inhibitory activity (IC50 > 7.8 microM) against the enzyme, whereas, compounds 1a-c as the methyl alpha-glycosides were found to be practically inactive (IC50 > 100 microM).
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PMID:Chemoenzymatic synthesis of neuraminic acid analogs structurally varied at C-5 and C-9 as potential inhibitors of the sialidase from influenza virus. 858 91

Trypanosoma brucei is a unicellular parasite that is transmitted from one mammalian host to the next by tsetse flies. The expression of many trypanosome genes is regulated during the life cycle but there is no evidence for developmental control of transcription by RNA polymerase II. T. brucei expresses at least two hexose transporter mRNAs that are developmentally regulated; we show here that specific portions of the 3'-untranslated regions are responsible for the differential expression. Different trypanosome 3'-untranslated regions, from surface protein, phosphoglycerate kinase and aldolase genes as well as the hexose transporter genes, conferred a spectrum of levels of reporter gene expression, and these activities differed between bloodstream forms and the procyclic forms that replicate in the tsetse vector. Experiments with permanently transformed cell lines showed that regulation occurs at the mRNA level. The results suggest that post-transcriptional control of mRNAs in trypanosomatids operates at several levels, and that it will not always be possible to attribute all the regulation to short RNA motifs.
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PMID:Role of 3'-untranslated regions in the regulation of hexose transporter mRNAs in Trypanosoma brucei. 872 Jan 70

The kinetic and equilibrium isotope effects on the fructose-1, 6-bisphosphate aldolase reaction have been determined using the rabbit muscle enzyme. The natural 13C abundance for both atoms participating in the bond splitting were measured in position C-1 of dihydroxyacetone phosphate and glyceraldehyde 3-P after irreversible conversion to glycerol-3-P and 3-phosphoglycerate, respectively, and chemical degradation. The carbon isotope effects were determined comparing the 13C content of the corresponding positions after partial and complete turnover, and after complete equilibration of the reactants. 13(Vmax/Km) on C-3 was 1.016 +/- 0.007 and 0.997 +/- 0.009 on position C-4, and the equilibrium isotope effects K12/K13 on these positions were 1.0036 +/- 0.0002 and 1.0049 +/- 0.0001. The observed kinetic isotope effect on C-3 is discussed to originate from the formation of the enamine, which comes to equilibrium before the rate determining release of glyceraldehyde 3-P from the ternary complex. The equilibrium isotope effect is seen as the reason for an earlier-found relative 13C enrichment in position C-3 and C-4 of glucose and for varying enrichments in 13C of carbohydrates from different compartments of cells. The kinetic isotope effect is suggested to cause 13C discriminations in the C-3 pool in context with the hexose formation in competition with other dihydroxyacetone phosphate turnover reactions.
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PMID:Carbon isotope effects on the fructose-1,6-bisphosphate aldolase reaction, origin for non-statistical 13C distributions in carbohydrates. 903 36

The generation of 13C-labeled D-glucose isotopomers by rat hepatocytes incubated for 30 or 120 min in the presence of 10 mM [3-(13)C]pyruvate was assessed by 13C NMR. The amount of C1-labeled D-glucose exceeded that of C2-labeled hexose, which was itself higher than that of C3-labeled D-glucose. A comparable hierarchy was observed in the C6-C5-C4 moiety of the hexose. The latter moiety of D-glucose was more efficiently labeled, however, than the C3-C2-C1 moiety. This finding is similar to that both previously reported and again observed in the present study when hepatocytes were exposed to [2(-13)C]pyruvate. These converging observations thus support the concept of enzyme-to-enzyme channeling of D-glyceraldehyde 3-phosphate between glyceraldehyde-3-phosphate dehydrogenase and phospho-fructoaldolase.
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PMID:Asymmetrical labeling of D-glucose generated from [3(-13)C]pyruvate in rat hepatocytes. 925 88

The enzymatic synthesis of 2-keto-3-deoxy-D-glycero-D-galacto-nonopyranulosonic acid (KDN) starting from D-mannose and pyruvic acid using Neu5Ac-aldolase has been scaled up. A repetitive batch ultrafiltration bioreactor was used for the KDN synthesis on 100 g scale with a conversion of up to 85%. Furthermore, a 440 mL pilot-scale enzyme membrane reactor (EMR) was performed for the continuous production of KDN. Conversion of mannose was 75% at a space--time yield of 375 g/(L d). KDN was advanteageously isolated by crystallization with an overall yield of 75%.
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PMID:Enzymatic large-scale production of 2-keto-3-deoxy-D-glycero-D-galacto-nonopyranulosonic acid in enzyme membrane reactors. 941 39

Class I fructose-1,6-bis(phosphate) aldolase is a glycolytic enzyme that catalyzes the cleavage of fructose 1,6-bis(phosphate) through a covalent Schiff base intermediate. Although the atomic structure of this enzyme is known, assigning catalytic roles to the various enzymic active-site residues has been hampered by the lack of a structure for the enzyme-substrate complex. A mutant aldolase, K146A, is unable to cleave the C3-C4 bond of the hexose while retaining the ability to form the covalent intermediate, although at a greatly diminished rate. The structure of rabbit muscle K146A-aldolase A, in complex with its native substrate, fructose 1,6-bis(phosphate), is determined to 2.3 A resolution by molecular replacement. The density at the hexose binding site differs between subunits of the tetramer, in that two sites show greater occupancy relative to the other two. The hexose is bound in its linear, open conformation, but not covalently linked to the Schiff base-forming Lys-229. Therefore, this structure most likely represents the bound complex of hexose just after hemiketal hydrolysis and prior to Schiff base formation. The C1-phosphate binding site involves the three backbone nitrogens of Ser-271, Gly-272, and Gly-302, and the epsilon-amino group of Lys-229. This is the same binding site previously found for the analogous phosphate of the product DHAP. The C6-phosphate binding site involves three basic side chains, Arg-303, Arg-42, and Lys-41. The residues closest to Lys-229 were relatively unchanged in position when compared to the unbound wild-type structure. The major differences between the bound and unbound enzyme structures were observed in the positions of Lys-107, Arg-303, and Arg-42, with the greatest difference in the change in conformation of Arg-303. Site-directed mutagenesis was performed on those residues with different conformations in bound versus unbound enzyme. The kinetic constants of these mutant enzymes with the substrates fructose 1, 6-bis(phosphate) and fructose 1-phosphate are consistent with their ligand interactions as revealed by the structure reported here, including differing effects on k(cat) and K(m) between the two substrates depending on whether the mutations affect C6-phosphate binding. In the unbound state, Arg-303 forms a salt bridge with Glu-34, and in the liganded structure it interacts closely with the substrate C6-phosphate. The position of the sugar in the binding site would require a large movement prior to achieving the proper position for covalent catalysis with the Schiff base-forming Lys-229. The movement most likely involves a change in the location of the more loosely bound C6-phosphate. This result suggests that the substrate has one position in the Michaelis complex and another in the covalent complex. Such movement could trigger conformational changes in the carboxyl-terminal region, which has been implicated in substrate specificity.
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PMID:Structure of a fructose-1,6-bis(phosphate) aldolase liganded to its natural substrate in a cleavage-defective mutant at 2.3 A(,). 1050 35

Various D-fructose analogues modified at C-1 or C-6 positions were synthesized from D-glucose by taking advantage of the Amadori rearrangement or using the aldol condensation between dihydroxyacetone phosphate and appropriate aldehyde catalyzed by fructose 1,6-diphosphate aldolase from rabbit muscle. The affinities of the analogues for the glucose transporter expressed in the mammalian form of Trypanosoma brucei were determined by inhibition of radiolabelled 2-deoxy-D-glucose (2-DOG) transport using zero-trans kinetic analysis. Interestingly, the analogues bearing an aromatic group (i.e. a fluorescence marker) at C-1 or C-6 positions present comparable apparent affinities to D-fructose for the transporter. This result could find applications for hexose transport studies and also provides criteria for the design of glucose import inhibitors.
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PMID:Chemical and enzymatic synthesis of fructose analogues as probes for import studies by the hexose transporter in parasites. 1081 60

The synthesis of 3-azido-3-deoxy, 3-amino-3-deoxy and 3-N-tert-butyloxycarbonyl-3-deoxy derivatives of 2-acetamido-2-deoxy-alpha,beta-D-mannose (N-acetyl-alpha,beta-D-mannosamine, ManNAc), is presented. The 3-azido-3-deoxy- and 3-N-tert-butyloxycarbonyl compounds were further characterised as their peracetates. A preliminary study has found that these C-3 nitrogen-substituted derivatives of ManNAc not to be substrates for Neu5Ac aldolase.
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PMID:Synthesis of C-3 nitrogen-containing derivatives of N-acetyl-alpha,beta-D-mannosamine as substrates for N-acetylneuraminic acid aldolase. 1143 70

d-Arabinose is a major sugar in the cell wall polysaccharides of Mycobacterium tuberculosis and other mycobacterial species. The reactions involved in the biosynthesis and activation of d-arabinose represent excellent potential sites for drug intervention since d-arabinose is not found in mammalian cells, and the cell wall arabinomannan and/or arabinogalactan appear to be essential for cell survival. Since the pathway involved in conversion of d-glucose to d-arabinose is unknown, we incubated cells of Mycobacterium smegmatis individually with [1-(14)C]glucose, [3,4-(14)C]glucose, and [6-(14)C]glucose and compared the specific activities of the cell wall-bound arabinose. Although the specific activity of the arabinose was about 25% lower with [6-(14)C]glucose than with other labels, there did not appear to be selective loss of either carbon 1 or carbon 6, suggesting that arabinose was not formed by loss of carbon 1 of glucose via the oxidative step of the pentose phosphate pathway, or by loss of carbon 6 in the uronic acid pathway. Similar labeling patterns were observed with ribose isolated from the nucleic acid fraction. Since these results suggested an unusual pathway of pentose formation, labeling studies were also done with [1-(13)C]glucose, [2-(13)C]glucose, and [6-(13)C]glucose and the cell wall arabinose was examined by NMR analysis. This method allows one to determine the relative (13)C content in each carbon of the arabinose. The labeling patterns suggested that the most likely pathway was condensation of carbons 1 and 2 of fructose 6-phosphate produced by the transaldolase reaction with carbons 4, 5, and 6 (i.e., glyceraldehyde 3-phosphate) formed by fructose-1,6 bisphosphate aldolase. Cell-free enzyme extracts of M. smegmatis were incubated with ribose 5-phosphate, xylulose 5-phosphate, and d-arabinose 5-phosphate under a variety of experimental conditions. Although the ribose 5-phosphate and xylulose 5-phosphate were converted to other pentoses and hexoses, no arabinose 5-phosphate (or free arabinose) was detected in any of these reactions. In addition, these enzyme extracts did not convert arabinose 5-phosphate to any other pentose or hexose. In addition, incubation of [(14)C]glucose 6-phosphate and various nucleoside triphosphates (ATP, CTP, GTP, TTP, and UTP) with cytosolic or membrane fractions from the mycobacterial cells did not result in formation of a nucleotide form of arabinose, although other radioactive sugars including rhamnose and galactose were found in the nucleotide fraction. Furthermore, no radioactive arabinose was found in the nucleotide fraction isolated from M. smegmatis cells grown in [(3)H]glucose, nor was arabinose detected in a large-scale extraction of the sugar nucleotide fraction from 300 g of cells. The logical conclusion from these studies is that d-arabinose is probably produced from d-ribose by epimerization of carbon 2 of the ribose moiety of polyprenylphosphate-ribose to form polyprenylphosphate-arabinose, which is then used as the precursor for formation of arabinosyl polymers.
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PMID:Biosynthesis of d-arabinose in Mycobacterium smegmatis: specific labeling from d-glucose. 1183 54


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