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Query: UNIPROT:P06889 (Mol)
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We have studied the effects of insulin on several aspects of cell metabolism in the insulin-sensitive, nonfusing muscle cell line BC3H-1. In the absence of exogenous hexose, insulin did not alter basal glycogen synthase percentage I activity, or attenuate the increase in intracellular cAMP content, the activation of glycogen phosphorylase a, or the decrease in glycogen synthase I brought about by beta-adrenergic receptor activation with epinephrine. In contrast, both insulin and the tumor-promoting phorbol ester, tetradecanoylyl phorbol acetate markedly increased mitochondrial pyruvate dehydrogenase activity in the absence of hexose. Both glycogen synthase phosphatase and glycogen synthase kinase activities were present in BC3H-1 cell extracts and were regulated in the expected manner by glucose 6-phosphate and cAMP, respectively. Since the pattern of partial insulin resistance seen in BC3H-1 myocytes would require that several potentially insulin-sensitive enzymes be insensitive to insulin-generated signals, the most likely explanation for these data is that the myocytes are defective in some mechanism of insulin signaling which is independent of the mechanism for pyruvate dehydrogenase activation.
Mol Pharmacol 1986 Dec
PMID:Hexose-independent activation of glycogen synthase and pyruvate dehydrogenase by insulin is dissociated in the mouse BC3H-1 cell line. 243 Dec 65

We report the functional expression of two different mammalian facilitative glucose transporters in Xenopus oocytes. The RNAs encoding the rat brain and liver glucose transporters were transcribed in vitro and microinjected into Xenopus oocytes. Microinjected cells showed a marked increase in 2-deoxy-D-glucose uptake as compared with controls injected with water. 2-Deoxy-D-glucose uptake increased during the 5 days after microinjection of the RNAs, and the microinjected RNAs were stable for at least 3 days. The expression of functional glucose transporters was dependent on the amount of RNA injected. The oocyte-expressed transporters could be immunoprecipitated with anti-brain and anti-liver glucose transporter-specific antibodies. Uninjected oocytes expressed an endogenous transporter that appeared to be stereospecific and inhibitable by cytochalasin B. This transporter was kinetically and immunologically distinguishable from both rat brain and liver glucose transporters. The uniqueness of this transporter was confirmed by Northern (RNA) blot analysis. The endogenous oocyte transporter was responsive to insulin and to insulinlike growth factor I. Most interestingly, both the rat brain and liver glucose transporters, which were not insulin sensitive in the tissues from which they were cloned, responded to insulin in the oocyte similarly to the endogenous oocyte transporter. These data suggest that the insulin responsiveness of a given glucose transporter depends on the type of cell in which the protein is expressed. The expression of hexose transporters in the microinjected oocytes may help to identify tissue-specific molecules involved in hormonal alterations in hexose transport activity.
Mol Cell Biol 1989 Oct
PMID:Functional expression of mammalian glucose transporters in Xenopus laevis oocytes: evidence for cell-dependent insulin sensitivity. 247 21

The effect of cAMP on glucose transport was studied in fibroblastic cells. Incubation of confluent NIH3T3 cells for 6 h in the presence of cholera toxin (10 ng/ml) and 3-isobutyl-1-methylxanthine [(IBMX) 0.2 mM] or 8-bromo-cAMP (0.3 mM) and IBMX resulted in a 4-fold increase in the rate of deoxyglucose uptake; no change in hexose transport could be detected after treatment for 30 min. Either cholera toxin (0.3 ng/ml-30 ng/ml) or 8-bromo-cAMP (30 microM-3 mM) increased the expression of the mRNA encoding the glucose transporter (GT) protein, as determined by hybridization of size-fractionated total RNA to a rat brain GT cDNA. Activation of adenylate cyclase by forskolin also rapidly induced a 4- to 10-fold increase in GT mRNA. The rise in the level of GT mRNA was maximal 3-4 h after addition of the drug, and returned to basal values by 16 h. The stimulation was concentration dependent, with forskolin producing a maximal effect at 30 microM. The effect of a submaximal concentration (1 microM) of forskolin was greatly enhanced in the presence of IBMX (0.2 mM), which alone had little effect on GT mRNA levels. The forskolin-stimulated increase in GT mRNA was not blocked by inhibition of protein synthesis by cycloheximide (10 micrograms/ml) or anisomycin (100 microM). The involvement of GT gene transcription was assessed by the nuclear run-on assay. Treatment of the cells with 30 microM forskolin increased transcription 10-fold within 30 min; the activation was not blocked by cycloheximide.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1989 Sep
PMID:The regulation of glucose transporter gene expression by cyclic adenosine monophosphate in NIH3T3 fibroblasts. 248 19

The reversible binding of phage G13, a phi X174-like single-strand DNA phage, to a 3H-labelled nonasaccharide from the lipopolysaccharide of its natural host Escherichia coli C was studied with equilibrium dialysis. The binding constant (Ka) was determined to 1.3 x 10(7) M-1 in Scatchard and Lineweaver-Burk plots. Approximately one saccharide bound per G13 phage particle which suggests that only one of the 12 spikes in each G13 virion was engaged in the phage/receptor saccharide interaction. Equilibrium dialysis inhibition experiments with saccharides from lipopolysaccharides of an isogenic series of Salmonella typhimurium mutants showed that hepta- and pentasaccharides from two G13-sensitive bacteria, i.e., with efficiencies of plating of 0.1-1.0 compared to E. coli C, were efficient inhibitors with Ka-values greater than or equal to 1.2 x 10(7) M-1. The octa- and hexasaccharides from two G13 resistant strains, with efficiency of plating less than or equal to x 10(-4), were either greater than 1000-fold or greater than 15-fold less efficient as inhibitors with Ka-values less than or equal to 8.8 x 10(5) M-1. The results show that phage G13 binds in a specific and reversible way to penta-, hepta-, and nonasaccharides from G13 sensitive bacteria with the specificity residing in the hexose and heptose region of the core lipopolysaccharide.
J Mol Recognit 1989 Jul
PMID:Interaction between phage G13 and its oligosaccharide receptor studied by equilibrium dialysis. 270 69

The preferred conformation of the hexose and heptose regions of core saccharides from Enterobacteriaceae lipopolysaccharides was calculated. The Hard Sphere Exo Anomeric (HSEA) approach was used and the minimum energy conformation of the Salmonella typhimurium and Escherichia coli R1, R2, R3, R4 and K12 cores calculated. The results indicate that most of the cores are sterically crowded, with small degrees of freedom, and that the hexose and heptose parts form two separate regions. The core structures exhibit a 'front'-side and a 'back'-side, the former being similar for all the structures and the latter being characteristic for each core type.
J Mol Recognit 1989 Jul
PMID:The conformation of core oligosaccharides from Escherichia coli and Salmonella typhimurium lipopolysaccharides as predicted by semi-empirical calculations. 270 70

The interaction between phage G13 and different bacterial and synthetic oligosaccharides has been studied using equilibrium dialysis inhibition. The results, and conformational analysis of the oligosaccharides, make us conclude that the phage G13 carbohydrate receptor is a conformational domain involving three sugar residues. The following trisaccharide elements contain the domain: alpha-D-Galp-(1----3)-[alpha-D-Galp-(1----6)]-alpha-D-Glcp, alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)-alpha-D-Manp , and alpha-D-Glcp-(1----3)-[L-gly-alpha-D-man-Hepp-(1----7)]-L-gly-alph a-D- man-Hepp. Thus two structures, either a hexose substituted with alpha-D-glycopyranosyl groups in the 3- and 6-positions, or a heptose substituted with such groups in the 3- and 7-positions are functional G13 binding sites. Such domains are present in several cores of lipopolysaccharides from Salmonella and Escherichia coli species. Some cores, e.g. those from S. typhimurium chemotypes Ra, Rb1 and Rb2, contain two such domains. The identification of two G13 receptor domains within different core saccharides could explain the broad host range of this phage.
J Mol Recognit 1989 Jul
PMID:Definition of the phage G13 receptor as structural domains of trisaccharides in Salmonella and Escherichia coli core oligosaccharides. 270 71

p-Chloromercuribenzoate alters various reactions of rat liver glucose (hexose phosphate) dehydrogenase differently. The reagent has little effect on the glucose: NAD or the glucose: NADP oxidoreductases, doubles the rates of oxidations of galactose-6-phosphate and glucose-6-phosphate by NADP and greatly stimulates the oxidations of glucose-6-phosphate and galactose-6-phosphate by NAD. The reagent appears to react with a sulfhydryl group of the enzyme since activation is reversed and prevented by mercaptoethanol. The direct reaction of the reagent with the enzyme is indicated by its lower thermal stability in the presence of the p-chloromercuribenzoate. The size of the enzyme appears to be the same when determined by sucrose gradient centrifugation in the presence or absence of p-chloromercuribenzoate. In microsomes, the oxidation of NADH or NADPH hampers measurements of glucose dehydrogenase. Since p-chloromercuribenzoate inhibits microsomal oxidation of reduced nicontinamide nucleotides, it is possible to assay for glucose dehydrogenase accurately in the presence of the mercurial in microsomes and microsomal extracts and thus measure the effectiveness of a detergent in extracting the enzyme from microsomes.
Mol Cell Biochem 1989 Apr 11
PMID:The activation of glucose dehydrogenase by p-chloromercuribenzoate. 277 Jul 7

The metabolism by coronary microvascular endothelial cells (CMEC) of the heart typical substrates palmitate and lactate was compared to that of glucose and glutamine. Confluent cultures of CMEC were used. Palmitate oxidation was saturable and independent of the exogenous albumin concentration. Palmitate, 300 microM, lactate, 1 mM, and glutamine, 0.5 mM, were oxidized to 35, 46, and 56 nmol CO2/h x mg protein. These oxidation rates were decreased by 80, 66, and 48% in presence of 5 mM glucose. The largest energy yield was obtained by glycolytic breakdown of glucose. Glucose, 5 mM, was degraded to lactate by 99%, and oxidized in the Krebs cycle by only 0.04%. 1% was catabolized via the hexose monophosphate pathway. The rate of glucose oxidation in the Krebs cycle could be 30-fold increased by the uncoupler 2,4-dinitrophenol, 30 microM. At concentrations lower than 1 mM the amount of glucose oxidized in the Krebs cycle also grew, indicating existence of the Crabtree effect. The energy demand of CMEC seems to be of the same order as that of the arrested heart.
Mol Cell Biochem
PMID:Fatty acids are not an important fuel for coronary microvascular endothelial cells. 277 44

The beta-adrenergic agonist 1-isoproterenol induced an early (less than 1 min) stimulation of endocytosis, amino acid transport and hexose transport, monitored by the temperature-sensitive uptake of horseradish peroxidase, alpha-aminoisobutyrate and 2-deoxyglucose, respectively, in rat ventricle cubes. This stimulation was time- and concentration-dependent and was maximum at 10(-8) M isoproterenol. The beta-adrenergic antagonist propranolol blocked isoproterenol stimulation of membrane transport, thereby confirming beta-adrenoceptor mediation; 2.5 mM EGTA, 1 mM LaCl2 and 100 microM verapamil blocked the hormonal response without affecting basal transport. The calcium ionophore A23187 caused an acute stimulation of endocytosis, hexose and amino acid transport. Isoproterenol rapidly (less than 30 s) stimulated 45Ca2+ influx. These data suggest that stimulus-response (stimulus-"transport") coupling is mediated by a rise in cytosolic Ca2+ concentration. A rapid (less than 30 to 60 s) increase in ornithine decarboxylase (ODC) activity, followed by an early (less than 1 to 2 min), sustained increase in putrescine, spermidine and spermine concentrations was evoked by 10(-7) M isoproterenol. The ODC inhibitor alpha-difluoromethylornithine (DFMO, 5 mM) suppressed the isoproterenol-induced increase in ODC and polyamine levels and the stimulation of 45Ca influx, endocytosis, hexose transport, and amino acid transport. Putrescine (0.5 mM) negated DFMO inhibition and restored the increase in polyamines, 45Ca influx, endocytosis, and transport of hexose and amino acid. These data suggest that polyamine synthesis is involved in isoproterenol stimulation of Ca2+ influx and membrane transport functions in ventricular myocardium. These findings are consistent with a model for signal transduction and stimulus-response coupling in which polyamines function as intracellular messengers to generate cytosolic Ca2+ signals by stimulating Ca2+ influx.
J Mol Cell Cardiol 1988 Sep
PMID:The role of polyamines in beta-adrenergic stimulation of calcium influx and membrane transport in rat heart. 285 23

Gas chromatographic (GC), mass spectrometric (MS), lectin binding and enzymatic analyses of the carbohydrates from Giardia cyst walls, intact cysts and trophozoites were performed to investigate the carbohydrate composition of Giardia cyst walls and to test the hypothesis that the Giardia cyst wall is composed largely of chitin. Galactosamine, verified by MS, was present in Giardia cyst walls and intact cysts (ca. 47 nmol 10(-6) cysts). Since not even trace amounts of it were detected in trophozoites by either GC or lectin binding, galactosamine is hypothesized to be a cyst wall-specific amino hexose. Based on the putative binding affinity of Phaseolus limensis lectin, galactosamine may be present in cyst walls as N-acetylgalactosamine. Neither glucosamine nor sialic acid were detected in as much as 11 mg dry weight of cysts, cyst walls, or trophozoites. Glucose, the most abundant carbohydrate, and ribose were detected in Giardia cysts and trophozoites. Galactose (ca. 10 nmol 10(-6) cysts) was detected in cysts but not in trophozoites. The lack of detectable levels of (1) glucosamine in cyst wall hydrolysates, (2) cyst staining by Calcofluor M2R, (3) endogenous chitinase activity and (4) N-acetylglucosamine when cysts served as a substrate for exogenous chitinase suggests that the Giardia cyst wall is not composed largely of chitin as previously reported. beta-N-Acetylgalactosaminidase, EC 3.2.1.32, activity was detected in cysts and trophozoites and represents the first carbohydrate splitting hydrolase detected in Giardia.
Mol Biochem Parasitol 1989 Jan 15
PMID:Giardia cyst wall-specific carbohydrate: evidence for the presence of galactosamine. 292 42


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