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1.
When given intraperitoneally to mice, lithium chloride decreased α-glucose-1,6-P2 in the brain to about 30% of normal. This may explain the observation that Li+ stimulates glucose utilization by brain and other tissues insofar as α-glucose-1,6-P2 inhibits animal hexokinase strongly. Glucose-1,6-P2 synthase activity of brain was much lower in Li+-animals when assayed without added divalent metal cofactor such as Mg2+ but the same with Mg2+ in the assay. This results because Li+ replaces the tightly bound activator, probably Zn2+. These results demonstrate the importance of α-glucose-1,6-P2 in regulation of hexokinase and suggest that normal energy metabolism of the brain may readily become sensitive to control by metal ion concentration. 相似文献
2.
Ligand-induced conformations of rat brain hexokinase: effects of glucose-6-phosphate and inorganic phosphate 总被引:1,自引:0,他引:1
J E Wilson 《Archives of biochemistry and biophysics》1973,159(1):543-549
Binding of glucose-6-P induces conformational change in rat brain hexokinase (ATP:d-hexose 6-phosphotransferase, EC 2.7.1.1) as indicated by decreased susceptibility to digestion by chymotrypsin and an increased sedimentation coefficient on sucrose density gradients. These effects are competitively reversed by Pi, as are solubilization (of the mitochondrial form of hexokinase) and inhibition by glucose-6-P. Thus, the observed conformational changes are likely to be directly related to the effect of these ligands on catalytic activity and the interaction of the hexokinase with the mitochondrial membrane.Both glucose-6-P and Pi stabilize the enzyme against heat inactivation; this effect, as well as the effect of glucose-6-P on inactivation by chymotrypsin, have been used to estimate the dissociation constants for the complexes of hexokinase with glucose-6-P and Pi; the values are 7–8 μm, and 0.25 mm, respectively.These observations are consistent with a model in which brain hexokinase may exist in two distinct conformations, rapidly and reversibly interconvertible. The effect of glucose-6-P and Pi are explained by highly preferential binding to one or the other of these conformations. 相似文献
3.
A specific spectrophotometric determination of β-glucose-1-phosphate has been devised. It allows β-glucose-1-phosphate to be measured in the presence of α-glucose-1-phosphate and of a one hundred-fold excess of glucose-6-phosphate. Phosphoglucomutase for β-glucose-1-phosphate obtained from cells of Euglena gracilis var. bacillaris must be prepared for the assay. 相似文献
4.
Two mechanisms have been suggested to account for the regulation of brain hexokinase by glucose 6-phosphate. One mechanism places glucose-6-P at an allosteric site, remote from the active site, while the second describes glucose-6-P as a simple product inhibitor of the enzyme, binding at the γ phosphate subsite within the ATP locus of the active site. To distinguish between these possibilities, we have undertaken a study of the back reaction of hexokinase I. Our data indicate that glucose-6-P displays classical Michaelis-Menten kinetics with brain hexokinase. This finding is consistent only with the high-affinity glucose-6-P site on the enzyme being the catalytic site. The dissociation constant, estimated from the initial-rate experiments is approximately 25 μm, a value that agrees well with the inhibition constant for glucose-6-P in the forward direction. These findings are consistent with an earlier model (W. R. Ellison, J. D. Lueck and H. J. Fromm, (1975) J. Biol. Chem.250, 1864–1871), which maintains that glucose-6-P inhibition of brain hexokinase is a manifestation of product inhibition. In a recent paper, Lazo et al. (P. A. Lazo, A. Sols, and J. E. Wilson, (1980) J. Biol. Chem.255, 7548–7551) reported data obtained from binding studies with rat brain hexokinase at an elevated (250 μm) level of glucose-6-P. These authors believe that their results indicate multiple binding of glucose-6-P to the enzyme and interpret the data in terms of a high-affinity allosteric site and a low-affinity catalytic site. Our results are at variance with this interpretation and are consistent only with the high-affinity site for glucose-6-P on brain hexokinase being the active site. 相似文献
5.
Poonam Talwar Salotra Vishwa Nath Singh 《Archives of biochemistry and biophysics》1982,216(2):758-764
The subcellular distribution and isozyme pattern of hexokinase in rat lung were studied. Of the total hexokinase activity of lung, one-third was bound to mitochondria and one-third of the mitochondrial activity was in a latent form. The overt-bound mitochondrial hexokinase was specifically solubilized by physiological concentrations of glucose 6-phosphate and ATP. Inorganic phosphate partially prevented the solubilization by glucose 6-phosphate (Glc 6-P), whereas Mg2+ ions promoted rebinding of the solubilized enzyme to mitochondria. Thus, the distribution of hexokinase between soluble and particulate forms in vivo is expected to be controlled by the relative concentrations of Glc 6-P, ATP, Pi, and Mg2+. Study of the isozyme pattern showed that hexokinase types I, II, and III constitute the cell-sap enzyme of lung. The overt and latent hexokinase activities could be separately isolated by successive treatments of mitochondria with Glc 6-P and Triton X-100. The overt-bound activity consisted primarily of hexokinase type I, with a small proportion of type II isozyme. The latent activity, on the other hand, exclusively consisted of type I isozyme. Type I hexokinase, the predominant isozyme in lung, was strongly inhibited by intracellular concentration of Glc 6-P and this inhibition was counteracted by Pi. The bound form of hexokinase exhibited a significantly higher apparent Ki for Glc 6-P inhibition and a lower apparent Km for ATP as compared to the soluble form. Thus, the particulate form of hexokinase is expected to promote glycolysis and may provide a mechanism for the high rate of aerobic glycolysis in lung. 相似文献
6.
《Biochimica et Biophysica Acta (BBA) - Enzymology》1981,657(2):468-481
Two major hexokinases (ATP: d-hexose 6-phosphotransferases, EC 2.7.1.1) have been identified in tissues of Homarus americanus (lobster) and separated from each other by DEAE-cellulose ion-exchange chromatography and by polyacrylamide gel electrophoresis. The molecular weight of each, determined by gel filtration, is about 50 000.Hexokinase II, named for its column elution order, resembles hexokinase isozymes I and II of vertebrates. Km values jfor glucose, mannose and fructose are 0.08, 0.13 and 6.7 mM, respectively. It is strongly inhibited by the reaction products, ADP and glucose-6-P (Ki = 0.8 mM).Hexokinase I appears to be different from any animal hexokinase previously described. It has a high affinity for mannose and fructose and low affinity for glucose. Km values are 6, 0.07 and 1.2 mM and relative maximum rates 100, 520 and 1070 for glucose, mannose and fructose, respectively. Hexokinase I is not inhibited by physiological concentrations of ATP nor by glucose-6-P, mannose-6-P or fructose-6-P even at high concentrations. Both enzymes occur in muscle at about 10% of the concentration found in the hepatopancreas.The use of Leuconostoc mesenteroides glucose-6-phosphate dehydrogenase (d-glucose-6-phosphate: NADP+ 1-oxidoreductase, EC 1.1.1.49), with NAD as cofactor, is recommended for measuring hexokinases in crude tissue preparations to avoid the variable further reduction of nucleotide caused by the action of 6-phosphogluconate dehydrogenase when NADP is used with yeast glucose-6-phosphate dehydrogenase. 相似文献
7.
Kang HK Cha H Yang TJ Park JT Lee S Kim YW Auh JH Okada Y Kim JW Cha J Kim CH Park KH 《Biochemical and biophysical research communications》2008,366(1):98-103
Di-O-α-maltosyl-β-cyclodextrin ((G2)2-β-CD) was synthesized from 6-O-α-maltosyl-β-cyclodextrin (G2-β-CD) via a transglycosylation reaction catalyzed by TreX, a debranching enzyme from Sulfolobus solfataricus P2. TreX showed no activity toward glucosyl-β-CD, but a transfer product (1) was detected when the enzyme was incubated with maltosyl-β-CD, indicating specificity for a branched glucosyl chain bigger than DP2. Analysis of the structure of the transfer product (1) using MALDI-TOF/MS and isoamylase or glucoamylase treatment revealed it to be dimaltosyl-β-CD, suggesting that TreX transferred the maltosyl residue of a G2-β-CD to another molecule of G2-β-CD by forming an α-1,6-glucosidic linkage. When [14C]-maltose and maltosyl-β-CD were reacted with the enzyme, the radiogram showed no labeled dimaltosyl-β-CD; no condensation product between the two substrates was detected, indicating that the synthesis of dimaltosyl-β-CD occurred exclusively via transglycosylation of an α-1,6-glucosidic linkage. Based on the HPLC elution profile, the transfer product (1) was identified to be isomers of 61,63- and 61,64-dimaltosyl-β-CD. Inhibition studies with β-CD on the transglycosylation activity revealed that β-CD was a mixed-type inhibitor, with a Ki value of 55.6 μmol/mL. Thus, dimaltosyl-β-CD can be more efficiently synthesized by a transglycosylation reaction with TreX in the absence of β-CD. Our findings suggest that the high yield of (G2)2-β-CD from G2-β-CD was based on both the transglycosylation action mode and elimination of the inhibitory effect of β-CD. 相似文献
8.
Jong-Hyun Jung Dong-Ho Seo James F. Holden Cheon-Seok Park 《Applied microbiology and biotechnology》2014,98(5):2121-2131
The deduced amino acid sequence from a gene of the hyperthermophilic archaeon Pyrococcus sp. ST04 (Py04_0872) contained a conserved glycoside hydrolase family 57 (GH57) motif, but showed <13 % sequence identity with other known Pyrococcus GH57 enzymes, such as 4-α-glucanotransferase (EC 2.4.1.25), amylopullulanase (EC 3.2.1.41), and branching enzyme (EC 2.4.1.18). This gene was cloned and expressed in Escherichia coli, and the recombinant product (P yrococcus sp. ST04 maltose-forming α-amylase, PSMA) was a novel 70-kDa maltose-forming α-amylase. PSMA only recognized maltose (G2) units with α-1,4 and α-1,6 linkages in polysaccharides (e.g., starch, amylopectin, and glycogen) and hydrolyzed pullulan very poorly. G2 was the primary end product of hydrolysis. Branched cyclodextrin (CD) was only hydrolyzed along its branched maltooligosaccharides. 6-O-glucosyl-β-cyclodextrin (G1-β-CD) and β-cyclodextrin (β-CD) were resistant to PSMA suggesting that PSMA is an exo-type glucan hydrolase with α-1,4- and α-1,6-glucan hydrolytic activities. The half-saturation value (K m) for the α-1,4 linkage of maltotriose (G3) was 8.4 mM while that of the α-1,6 linkage of 6-O-maltosyl-β-cyclodextrin (G2-β-CD) was 0.3 mM. The k cat values were 381.0 min?1 for G3 and 1,545.0 min?1 for G2-β-CD. The enzyme was inhibited competitively by the reaction product G2, and the K i constant was 0.7 mM. PSMA bridges the gap between amylases that hydrolyze larger maltodextrins and α-glucosidase that feeds G2 into glycolysis by hydrolyzing smaller glucans into G2 units. 相似文献
9.
The binding of glucose and glucose-6-P by pure rat brain hexokinase has been studied by using an ultrafiltration procedure [H. Paulus (1969) Anal. Biochem. 32, 91–100]. Each mole of enzyme (molecular weight 98,000) binds 1 mole of glucose or 1 mole of glucose-6-P. The dissociation constant for the enzyme-glucose complex (0.04 mm) is in excellent agreement with the kinetically determined Km for this substrate. The dissociation constant for the enzyme-glucose-6-P complex was estimated to be 1.3 μm, substantially lower than values of 7–8 μm obtained by alternative methods. This discrepancy appears to be due to retardation of the passage of the charged glucose-6-P through the ultrafiltration membrane, resulting in an effective increase in the ligand concentration at the membrane surface and thereby a decrease in the apparent dissociation constant. No appreciable retardation of the passage of the uncharged glucose molecule was observed.The binding of glucose-6-P (but not glucose) is prevented in the presence of Pi. This is in accord with a previously suggested model in which binding of Pi is considered to stabilize the enzyme in a conformation having little, if any, affinity for glucose-6-P.Serine was found as a C-terminal amino acid. The method used would not have detected C-terminal proline or tryptophan residues, and thus these cannot be excluded by the present experiments. However, in view of other results indicating that rat brain hexokinase consists of a single polypeptide chain, it seems probable that serine is indeed the only C-terminal amino acid in the molecule. 相似文献
10.
Synthesis of anomeric sulfonamides and their behaviour under radical-mediated bromination conditions
Katalin Czifrák 《Carbohydrate research》2009,344(3):269-5455
O-Peracetylated methyl 3-(d-glycopyranosylthio)propanoates of β-d-gluco, and α- and β-d-galacto configurations were oxidized to the corresponding S,S-dioxides (sulfones) by Oxone® or MCPBA. Oxidation of the β-d-gluco derivative with H2O2/Na2WO4 gave the corresponding S-oxide (sulfoxide). DBU-induced elimination of methyl acrylate from the β-d-gluco and β-d-galacto configured S,S-dioxides (sulfones) gave O-peracetylated β-d-glycopyranosyl-1-C-sulfinates which, on treatment with H2NOSO3H, furnished the corresponding β-d-glycopyranosyl-1-C-sulfonamides. Radical-mediated bromination of the protected methyl 3-(β-d-glycopyranosylthio)propanoate S,S-dioxides gave mixtures of 1-C- and 5-C-bromoglycosyl compounds. Similar brominations of the O-peracetylated β-d-glycopyranosyl-1-C-sulfonamides resulted in the formation of α-d-glycopyranosyl bromides and 1-C- and 5-C-bromoglycosyl sulfonamides. A rationale for these observations was proposed. Methyl 3-(β-d-glucopyranosylthio)propanoate, its S,S-dioxide, and β-d-glucopyranosyl-1-C-sulfonamide proved inefficient when tested as inhibitors of rabbit muscle glycogen phosphorylase b. 相似文献
11.
J E Wilson 《Archives of biochemistry and biophysics》1978,185(1):88-99
Various ligands of rat brain hexokinase (ATP:d-hexose 6-phosphotransferase, EC 2.7.1.1) have been found to protect the enzyme against either (or both) chymotryptic digestion or inactivation by glutaraldehyde. Using this protective effect, the Kd for various enzyme-ligand complexes has been estimated: hexokinase-Glc, Kd = 0.24 ± 0.03mM (chymotryptic digestion), Kd = 0.26 ± 0.07mM (glutaraldehyde inactivation); hexokinase-Glc-6- P, Kd = 0.041 ± 0.005m M (glutaraldehyde inactivation); hexokinase-ATP, Kd = 1.01 ± 0.28mM (chymotryptic digestion); hexokinase-ATP-Mg 2+, Kd = 0.07-0.08mM (chymotryptic digestion). Other nucleoside triphosphates (UTP, ITP, GTP, and CTP) were much less effective than ATP at protecting against chymotrypsin. Various hexoses were tested for their ability to protect against glutaraldehyde. Only ?good” substrates (mannose, 2-deoxyglucose) protected; nonsubstrates (galactose, arabinose) and N-acetylglucosamine, a competitive inhibitor of Glc binding, were not effective. Various hexose 6-phosphates were tested for their ability to protect against glutaraldehyde inactivation. Glc-6-P was much more effective than were mannose-6-P, galactose-6-P, or fructose-6-P. It was observed that ?good” substrates (Glc, mannose) increased the effectiveness of Glc-6-P at solubilizing the mitochondrial form of the enzyme; galactose and N-acetylglucosamine had no effect on solubilization by Glc-6-P. These results are taken as an indication of enhanced Glc-6-P binding in the presence of Glc, as previously reported by Ellison et al. (J. Biol. Chem., 250, 1864–1871, 1975). Along with previous studies on ligand-induced conformations and kinetics of this enzyme, these results form the basis for a new model for brain hexokinase. This model specifically takes into account the ligand-induced conformations at various points in the catalytic cycle and specifically accounts for the ability of various hexoses to serve as substrates and hexose 6-phosphates to serve as inhibitors in terms of their ability to induce specific conformations of the enzyme. The properties of the various conformations involved in the model are designated by a four-letter code which facilitates comparison and discussion. 相似文献
12.
A study of the sulfhydryl groups of rat brain hexokinase 总被引:1,自引:0,他引:1
Rat brain hexokinase (ATP: d-hexose-6-phosphotransferase, EC 2.7.1.1) is rapidly inactivated by reaction with 5,5′-dithiobis-(2-nitrobenzoate). The inactivation follows monophasic first-order kinetics in either the absence of ligands (k = 0.641 min?1 at 25 °C) or in the presence of saturating levels of ATP (free or complexed with Mg2+) or P1; the inactivation rate is slightly increased ( min ?1) in the presence of ATP or P1. In contrast, glucose and glucose-6-P markedly decrease the inactivation rate; inactivation in the presence of these ligands is biphasic, with two first-order rates ( min?1 and 0.01 min?1) being distinguishable.The enzyme contains 14 sulfhydryl groups which react with 5,5′-dithiobis-(2-nitrobenzoate); reaction of these groups in the native enzyme is complete after 2 hr at 25 °C, or in approx 5 min with the urea or guanidine-denatured enzyme. In the native enzyme, three classes of sulfhydryl groups are distinguishable and are designated as F-, I-, or S-type based on their fast (k ? 0.7 min?1), intermediate ( min?1), or slow ( min?1 rates of reaction with 5,5′-dithiobis-(2-nitrobenzoate). The correlation of inactivation rates with the rates for reaction of the I-type sulfhydryls indicates that the I-type sulfhydryls include residues necessary for catalytic activity. The F-type residues are clearly not required for activity.The effects of ATP, P1, glucose, and glucose-6-P on the reactivity of the sulfhydryls have been determined. As in the absence of ligands, S-, I-, and F-type sulfhydryls could be distinguished. In the presence of saturating concentrations of these ligands, the F, I, and S classes of sulfhydryls contained respectively: with ATP, 1, 4, and 7 residues; with P1, 1, 3, and 7 residues; with glucose, 1, 2, and 5 residues; with glucose-6-P, 1, 2, and 1 residues. Comparison with rate constants for inactivation in the presence of these ligands again indicated that I-type sulfhydryls were particularly important in maintenance of enzyme activity. The present results indicate considerable similarity between the reactivity of the sulfhydryl residues in rat brain hexokinase and the sulfhydryls of the bovine brain enzyme [V. D. Redkar and U. W. Kenkare (1972), J. Biol. Chem., 247, 7576–7584]. 相似文献
13.
David Cooper R. St. John Manley 《Biochimica et Biophysica Acta (BBA)/General Subjects》1975,381(1):78-96
An analysis has been made of the low molecular weight fraction present in the region of cellulose synthesis in Acetobacter xylinum suspensions.A number of nucleic acid bases, nucleosides and nucleotides, together with α-glucose 1-phosphate and UDPG, were detected in various extracts of washed cells supplied with glucose. Since glucose-6-P could be detected in extracts of ultrasonically disrupted cells, but not in extracts of whole cells, it was concluded that separate pools of hexose phosphate exist in A. xylinum. Preferential release of α-glucose-1-P, UDPG and nucleotides was observed during ethanol and EDTA treatment of bacteria. Electron microscopic examination of treated and untreated cells revealed that extensive modification of the cell wall region occured during such treatments. The results support the proposal that α-glucose-1-P, UDPG and nucleotide pools are localised in the cell envelope region, possibly in the periplasm, and that A. xylinum possesses a second permeability barrier outside the cytoplasmic membrane. Nucleic acid bases and nucleosides were observed to diffuse freely through the cell wall and accumulate in the medium, probably as the result of nucleic acid breakdown. The results imply that the effects of cell damage caused by the isolation of the bacteria from the surface pellicle of the culture medium, together with nutrient deprivation, should be considered in work using the non-proliferating system. A study of the variation in concentration with time of α-glucose-1-P and UDPG, during cellulose synthesis, indicated that both components mau play an immediate role in cellulose synthesis.Glycosylated lipid compounds were detected in both cell wall extracts and supernatant fluid, but it is not certain whether these compounds are constituents of the supernatant fluid in vivo. 相似文献
14.
Siddhartha Roy 《Analytical biochemistry》1983,133(2):292-295
A new continuous spectrophotometric assay is demonstrated for Escherichia coli alanyl-tRNA synthetase. It involves β-γ adenylyl imidophosphate as a substitute for ATP in the pyrophosphate exchange reaction. The net conversion of β-γ adenylyl imidophosphate to ATP can be linked to NADP reduction by hexokinase and glucose-6-P dehydrogenase catalyzed reactions, which can be monitored at 340 nm. This assay can be extended to other aminoacyl-tRNA synthetases which can use β-γ nonhydrolyzable analogs of ATP as an ATP substitute. 相似文献
15.
Regulation of ribulose-1,5-bisphosphate carboxylase from tobacco: changes in pH response and affinity for CO2 and Mg2+ induced by chloroplast intermediates 总被引:10,自引:0,他引:10
Ribulose-1,5-bisphosphate caryboxylase-oxygenase is activated by CO2 and Mg2+ in a process distinct from catalysis. The effect of chloroplast metabolites as they separately influenced either activation or catalysis of tobacco carboxylase was examined. Of the 28 metabolites examined, 13 effected activation of the carboxylase. The strongest positive effectors were NADPH, gluconate-6-P, glycerate-2-P, and glycerate-3-P. Negative effectors included ribose-5-P, fructose-6-P, glucose-6-P, and pyrophosphate. The concentration of CO2 or Mg2+ necessary to produce half-maximal activation is defined as Kact. NADPH and gluconate-6-P decreased the Kact(CO2) from 43 to 7.4 and 3.5 μm, respectively (pH 8.0, 5 mm MgCl2). They also decreased the Kact(M.g2+), but had little affect on the affinity of the enzyme for CO2 during the catalytic process. Increasing Mg2+ concentration decreased the Kact(CO2) and increasing CO2 concentration decreased the Kact-(Mg2+). NADP+ and gluconate-6-P also affected the pH profile of activation, shifting it toward lower pH values. Changes in activation had no effect on the pH profile for catalysis of CO2 fixation. Effectors influenced ribulose-1,5-bisphosphate oxygenase in a manner analogous to the carboxylase. At air levels of O2 and CO2, the ratio of carboxylase to oxygenase activity was not changed by the presence of effectors, including hydroxylamine. 相似文献
16.
dl-[1,6-14C]Lipoic acid was administered by intraperitoneal injection to rats at the level of 0.5 mg/100 g body weight. Approximately 56% of the radioactivity was recovered in the urine. When acidified and extracted with benzene, 92% of the radioactivity remained in the aqueous phase. Gel-filtration and paper chromatography were used to identify three of the compounds in the benzene extract as lipoic, bisnorlipoic and tetranorlipoic acids. In addition, a keto compound appears to be present. The aqueous phase contained several radioactive components separable by ion-exchange and paper chromatographies. Two of these compounds were identified as lipoate and β-hydroxybisnorlipoate. No evidence for oxidation of the dithiolane ring of lipoic acid was observed. dl-[7,8-14C]Lipoic acid was administered to rats under the same conditions. The urine contained 81% of the radioactivity, 72% of which remained in the aqueous phase and 28% was extracted into benzene. In contrast to over 30% of the label from dl-(1,6-14C] lipoate being expired as 14CO2, a negligible amount of 14CO2 was produced by rats injected with dl-[7,8-14C]lipoate. The catabolites identified were the same as those found using the 1,6-labeled lipoate. Another dithiolane-intact compound was also isolated. It appears that the rat, similar to Pseudomonas putida LP, metabolizes lipoate mainly via β-oxidation of the valeric acid side chain. 相似文献
17.
Corwin M. Nycholat 《Carbohydrate research》2009,344(12):1397-1411
A panel of six complementary monodeoxy and mono-O-methyl congeners of methyl β-d-mannopyranosyl-(1→2)-β-d-mannopyranoside (1) were synthesized by stereoselective glycosylation of monodeoxy and mono-O-methyl monosaccharide acceptors with a 2-O-acetyl-glucosyl trichloroacetimidate donor, followed by a two-step oxidation-reduction sequence at C-2′. The β-manno configurations of the final deprotected congeners 2-7 were confirmed by measurement of 1JC1,H1 heteronuclear and 3J1′,2′ homonuclear coupling constants. These disaccharide derivatives will be used to map the protective epitope recognized by a protective anti-Candida albicans monoclonal antibody C3.1 (IgG3) and to determine its key polar contacts with the binding site. 相似文献
18.
Corwin M. Nycholat 《Carbohydrate research》2009,344(5):555-569
A panel of six complementary monodeoxy and mono-O-methyl congeners of methyl β-d-mannopyranosyl-(1→2)-β-d-mannopyranoside (1) were synthesized by stereoselective glycosylation of monodeoxy and mono-O-methyl monosaccharide acceptors with a 2-O-acetyl-glucosyl trichloroacetimidate donor, followed by a two-step oxidation-reduction sequence at C-2′. The β-manno configuration of the final deprotected congeners 2-7 was confirmed by measurement of 1JC1,H1 heteronuclear and 3J1′,2′ homonuclear coupling constants. These disaccharide derivatives will be used to map the epitope recognized by a protective anti-Candida albicans monoclonal antibody C3.1 (IgG3) and to determine its key polar contacts with the binding site. 相似文献
19.
Hexokinase I (ATP:d-hexose 6-phosphotransferase, EC 2.7.1.1), a key regulatory glycolytic enzyme in certain tissues, is known to be markedly inhibited under physiological conditions. The action of the primary inhibitory effector, glucose-6-P, is reversed by inorganic orthophosphate (Pi). A molecular model for inhibition and deinhibition of hexokinase was recently proposed [Ellison, W. R., Lueck, J. D., and Fromm, H. J. (1975) J. Biol. Chem.250, 1864–1871]. One of the central assumptions of this model is that glucose-6-P is a normal product inhibitor of hexokinase. It has long been suggested that glucose-6-P is an allosteric inhibitor of hexokinase, whereas other sugar-phosphate products such as mannose-6-P are normal product inhibitors. In this report we investigated the kinetic mechanism of hexokinase action with mannose as substrate and mannose-6-P as an inhibitor. The data obtained show that there are no qualitative differences between glucose and mannose as substrates and glucose-6-P and mannose-6-P as inhibitors. Binding experiments indicate that glucose-6-P and mannose-6-P are competitive binding ligands with hexokinase I. Furthermore, the activation pattern observed with Pi and glucose-6-P inhibited hexokinase is also found with the mannose-6-P inhibited phosphotransferase. These findings suggest that the mechanism of inhibition of glucose-6-P and mannose-6-P represents a difference in degree rather than a difference in kind. An explanation of the results in terms of a stereochemical model is presented. 相似文献
20.
Evangelina Repetto Carla Marino M. Laura Uhrig Oscar Varela 《Bioorganic & medicinal chemistry》2009,17(7):2703-2711
Thiodisaccharides having β-d-Galf or α-l-Araf units as non-reducing end have been synthesized by the SnCl4- or MoO2Cl2-promoted thioglycosylation of per-O-benzoyl-d-galactofuranose (1), its 1-O-acetyl analogue 4, or per-O-acetyl-α-l-arabinofuranose (16) with 6-thioglucose or 6-thiogalactose derivatives. After convenient removal of the protecting groups, the free thiodisaccharides having the basic structure β-d-Galf(1→6)-6-thio-α-d-Glcp-OMe (5) or β-d-Galf(1→6)-6-thio-α-d-Galp-OMe (15) were obtained. The respective α-l-Araf analogues 18 and 20 were prepared similarly from 16. Alternatively, β-d-Galf(1→4)-4-thio-3-deoxy-α-l-Xylp-OiPr was synthesized by Michael addition to a sugar enone of 1-thio-β-d-Galf derivative, generated in situ from the glycosyl isothiourea derivative of 1. The free S-linked disaccharides were evaluated as inhibitors of the β-galactofuranosidase from Penicillium fellutanum, being 15 and 20 the more active inhibitors against this enzyme. 相似文献