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PubMed1988

Structure elucidation of the core regions from Citrobacter O4 and O36 lipopolysaccharides by chemical and enzymatic methods, gas chromatography/mass spectrometry, and NMR spectroscopy at 500 MHz.

Novel enterobacterial core oligosaccharides were isolated from Citrobacter O4 and O36 lipopolysaccharides, and their structures were determined by methylation analysis, Smith degradation and enzymatic degradations, gas chromatography/mass spectrometry, and two-dimensional phase-sensitive correlated, relayed coherence transfer, double-quantum, triple-quantum-filtered, and nuclear Overhauser effect (NOE) 1H NMR spectroscopy at 500 MHz. In the formulas, all hexose residues are D-hexopyranoses, and heptoses are L-glycero-D-manno-heptopyranoses; the alternative locations of the side-chain heptose and pyrophosphorylethanolamine (PPEtN) residues are marked by dashed lines; dOclA stands for 3-deoxy-D-manno-octulosonic acid. (formula; see text) Along with these complete cores, incomplete ones, lacking the hexosamine trisaccharides, occur in the lipopolysaccharides of both types. Qualitative NOE data were in good agreement with the minimum energy conformation of the above O36 oligosaccharide, calculated with the aid of the SUGAR program [Sundin, A., Carter, R. E., & Liljefors, T. (1988) J. Mol. Graphics (in press)].

Acetylglucosaminidase↗
PubMed1989

Gangliosides interact directly with plasminogen and urokinase and may mediate binding of these fibrinolytic components to cells.

Receptors for the fibrinolytic molecules plasminogen and urokinase are expressed at high capacity on a wide variety of peripheral blood cells and transformed cell lines. We have considered whether gangliosides, components of the outer leaflets of cell membranes, may modulate the interactions of these fibrinolytic ligands with cells. Radiolabeled plasminogen and urokinase bound directly to insolubilized gangliosides. The interactions were saturable and were 50% inhibited by 2.2 microM unlabeled plasminogen or 12 nM unlabeled urokinase, respectively. A panel of gangliosides inhibited binding of both ligands to U937 monocytoid cells, and the order of decreasing inhibitory effectiveness was GD1a greater than GM1 greater than GT1b greater than GM2, while GM3 was minimally effective. The individual components of gangliosides, hexoses, hexosamines, sialic acid, GM1 pentasaccharide, ceramides, and glucocerebrosides were ineffective in in inhibiting the binding of plasminogen and urokinase either to cells or to insolubilized gangliosides. Binding of both ligands to endothelial cells and granulocytes and binding of plasminogen to platelets were also inhibited by gangliosides. U937 cells were cultured with gangliosides to allow incorporation of these glycolipids into the cell membranes. After 3 days of culture, both urokinase binding and plasminogen binding to the cells became enhanced. These results suggest that gangliosides can directly bind to these fibrinolytic components and may mediate or modulate the interactions of plasminogen and urokinase with a variety of cell types.

Carbohydrates↗
PubMed1982

Biosynthesis of cell surface sulfated glycoproteins by cultured vascular endothelial cells.

Cultured vascular endothelial cells incorporate 35SO4 into a class of oligosaccharides which are N-glycosidically linked to cell-surface or extracellular proteins. This type of sulfated oligosaccharide was not synthesized by smooth muscle cell cultures and may represent sulfation of vascular tissue glycoproteins which are unique to endothelial cells. These endothelial cell 35S-labeled oligosaccharides are not released from the polypeptides under alkaline conditions that cleave O-glycosidically linked chains. The incorporation of both [3H]hexosamine and 35SO4 into these oligosaccharides is inhibited by tunicamycin, an antibiotic which inhibits protein N-glycosylation. 35S-Labeled oligosaccharides, isolated as glycopeptides, were resistant to a variety of chemical and enzymatic treatments which degraded vascular cell sulfated glycosaminoglycans but appear to contain terminal sialic acid residues. Endothelial cell sulfated oligosaccharide chains could also be distinguished from sulfated glycosaminoglycans by the apparent size and charge. Endothelial cells released or secreted 35S-labeled glycoproteins into the culture medium. These soluble 35S-labeled glycoproteins were partially purified by DEAE-cellulose chromatography and separated from the 35S-labeled proteoglycans, which are also released into the medium. The major 35S-labeled glycoproteins released from the cells had apparent molecular weights of 24 000--66 000. The cell-associated 35S-labeled glycoproteins, released with ethylenediaminetetraacetate or extracted with 0.5% octyl glucoside, were partially purified on DEAE-cellulose and had apparent molecular weights of 45 000--250 000.

Animals↗
PubMed1979

Enzymic O-glycosylation of synthetic peptides from sequences in basic myelin protein.

Nine synthetic peptides containing sequences in the region of a threonine residue at position 98 of bovine basic myelin protein were prepared by the Merrifield solid-phase method and tested for their ability to be glycosylated with [14C]uridinediphospho-N-acetylgalactosamine and a crude detergent-solubilized preparation of uridinediphospho-N-acetylgalactosamine:mucin polypeptide N-acetylgalactosaminyltransferase obtained from porcine submaxillary glands. The tetrapeptide Thr-Pro-Pro-Pro and all larger peptides containing this sequence were glycosylated. The glycosylation was greater for peptides containing residues N-terminal to the Thr-Pro-Pro-Pro. Under the conditions used, the peptide Val-Thr-Pro-Arg-Thr-Pro-Pro-Pro was glycoslyated twice as much as bovine basic myelin protein. Thr-Pro and Thr-Pro-Pro, as well as 10 other synthetic peptides which did not contain the Thr-Pro-Pro-Pro sequence, were not glycosylated. Treatment of the glycopeptide of Phe-Lys-Asn-Leu-Val-Thr-Pro-Arg-Thr-Pro-Pro-Pro-Ser with an alpha-N-acetylgalactosaminidase released N-acetylgalactosamine from the peptide, indicating that the hexosamine was covalently bonded to the peptide in an alpha linkage.

Amino Acid Sequence↗
PubMed1978

Isolation of six novel phosphoinositol-containing sphingolipids from tobacco leaves.

A concentrate of phosphosphingolipids from tobacco leaves has been resolved into two groups by chromatography on diethylaminoethylcellulose. The first group eluted contains no acetyl residues, whereas the second group contains one N-acetyl/mol of phosphorus. Three lipids from each group have been purified by chromatography on Porasil columns. The chemical composition of these six novel lipids shows them to be related to the previously characterized phosphosphingolipids PSL-I, N-acetylglucosamine[glucuronic acid, inositol phosphate]ceramide and PSL-II, glucosamine[glucuronic acid, inositol phosphate] ceramide [Kaul, K.,and Lester,R. L. (1975), Plant Physiol. 55, 120]. The novel lipids are: PSL-IA, PSL-I-[Ara2Gal2]; PSL-IB, PSL-I-[Ara3Gal2]; PSL-IC, PSL-I-[Ara4Gal2]; PSL-IIA, PSL-II-[Ara3Gal]; PSL-IIB, PSL-II-[Ara2or3Gal2]; PSL-IIC, PSL-II-[Ara2Gal2Man]. The unusual finding of unacetylated hexosamine in the PSL-II group of lipids appears not to be an artifact, as suggested by experiments involving rapid harvesting and processing of the tobacco leaves. Some of the fractions obtained by chromatography on diethylaminoethylcellulose appear to contain phosphosphingolipids with 16 or more sugar residues.

Phosphatidylinositols↗
PubMed1977

Lipoprotein lipase. Isolation and characterization of a second enzyme species from postheparin plasma.

A lipoprotein lipase species (mol wt 69 250) has been isolated from rat postheparin plasma, which differs from the low-molecular-weight species previously characterized in its amino acid composition and hexosamine content, and in its lower affinity for triglyceride-rich lipoprotein substrates. However, both enzymes are activated by the same coprotein (C-terminal glutamic acid, apo-C-2) from human very low density lipoprotein and have a similar specificity for lipid esters. Neither purified enzyme is activated by heparin. Both are inhibited by molar sodium chloride. Both enzyme species can be recovered from the same plasma samples. The possible relationship of these proteins to the different functional lipoprotein lipase activities of muscle and adipose tissues is discussed.

Amino Acids↗
PubMed1976

Characterization of human, bovine, and horse antithrombin III.

A comparison of the physical-chemical properties of human, bovine, and horse antithrombin III has been made. These three plasma proteins are strong inhibitors of bovine factor Xa and form a 1:1 molar complex with this coagulation enzyme. Human, bovine, and horse antithrombin III are glycoproteins containing hexose, hexosamine, and neuraminic acid. The total carbohydrate was 9, 12, and 16% for human, bovine, and horse antithrombin III, respectively. These proteins have a similar amino acid composition, although some monor variations were noted. Each antithrombin III is composed of a single polypeptide chain with an amino-terminal histidine residue. Of the first 17 amino-terminal residues, only three differences were noted between the three proteins. These occur in position 2 which is occupied by Gly, Arg, and Trp in human, bovine, and horse, respectively; position 6 which has a deletion in human antithrombin III; and position 8 where Ile in human and horse antithrombin III has been replaced by Val in the bovine preparation. The remainder of the first 17 residues is the same in all three proteins. The molecular weights for the bovine and horse preparation were 56 600 and 52 500, respectively, as determined by sedimentation equilibrium in the presence of guanidine hydrochloride. Some immunological cross-reactivity was also observed between the three different proteins.

Amino Acids↗
PubMed2004

Conformational analysis of chirally deuterated tunicamycin as an active site probe of UDP-N-acetylhexosamine:polyprenol-P N-acetylhexosamine-1-P translocases.

Tunicamycins are potent inhibitors of UDP-N-acetyl-D-hexosamine:polyprenol-phosphate N-acetylhexosamine-1-phosphate translocases (D-HexNAc-1-P translocases), a family of enzymes involved in bacterial cell wall synthesis and eukaryotic protein N-glycosylation. Structurally, tunicamycins consist of an 11-carbon dialdose core sugar called tunicamine that is N-linked at C-1' to uracil and O-linked at C-11' to N-acetylglucosamine (GlcNAc). The C-11' O-glycosidic linkage is highly unusual because it forms an alpha/beta anomeric-to-anomeric linkage to the 1-position of the GlcNAc residue. We have assigned the (1)H and (13)C NMR spectra of tunicamycin and have undertaken a conformational analysis from rotating angle nuclear Overhauser effect (ROESY) data. In addition, chirally deuterated tunicamycins produced by fermentation of Streptomyces chartreusis on chemically synthesized, monodeuterated (S-6)-[(2)H(1)]glucose have been used to assign the geminal H-6'a, H-6'b methylene bridge of the 11-carbon dialdose sugar, tunicamine. The tunicamine residue is shown to assume pseudo-D-ribofuranose and (4)C(1) pseudo-D-galactopyranosaminyl ring conformers. Conformation about the C-6' methylene bridge determines the relative orientation of these rings. The model predicts that tunicamycin forms a right-handed cupped structure, with the potential for divalent metal ion coordination at 5'-OH, 8'-OH, and the pseudogalactopyranosyl 7'-O ring oxygen. The formation of tunicamycin complexes with various divalent metal ions was confirmed experimentally by MALDI-TOF mass spectrometry. Our data support the hypothesis that tunicamycin is a structural analogue of the UDP-D-HexNAc substrate and is reversibly coordinated to the divalent metal cofactor in the D-HexNAc-1-P translocase active site.

Binding Sites↗
PubMed2002

Synthesis of 5-fluoro N-acetylglucosamine glycosides and pyrophosphates via epoxide fluoridolysis: versatile reagents for the study of glycoconjugate biochemistry.

Numerous carbohydrate-processing enzymes facilitate catalysis via stabilization of positive charges on or near the C-1, C-4, C-5, or C-6 positions. Substrate analogues differing only in the substitution of a fluorine for the axial C-5 hydrogen would possess reduced electron density at these positions and could be useful mechanistic probes of these enzymes. Introduction of this 5-fluoro substituent after radical halogenation was problematic because of the incompatibility of many protecting groups to the radical halogenation and the instability of the subsequent 5-fluoro hexosamines. Thus, to allow easy access to a wide variety of 5-fluoro glycosides and glycosyl phosphates, a versatile method for the introduction of the 5-fluoro group has been developed, the key step being the fluoridolysis of C-5, 6 epoxides. By use of this method, two fluorinated carbohydrates, uridine 5'-diphospho-5-fluoro-N-acetylglucosamine and octyl 5-fluoro-N-acetylglucosamine, have been synthesized. Initial biochemical investigations of these compounds show that 5-fluoro analogues are useful probes of transition-state charge development in several enzyme-catalyzed reactions.

Acetylglucosamine↗
PubMed1997

A new high molecular weight agglutinin from garlic (Allium sativum).

Erythrocyte agglutination by lectins from Allium sativum was inhibited only by mannose of the sugars tested. However, asialofetuin was more effective inhibitor of agglutination as compared to mannose. This led to the use of an asialofetuin-silica affinity column to isolate agglutinins of 110 and 25 kDa (ASA110 and ASA25). While ASA25 is a dimeric protein comprising of subunits of 12.5 and 13.0 kDa, ASA110 is a glycoprotein of two identical subunits of 47 kDa. ASA110 revealed to have a high content of aspartic acid, glycine, leucine and serine but low content of cysteine and methionine. It contains 14 residues of neutral sugars in addition to 43 residues of hexosamines per mole of lectin and requires metal ions for its functional conformation. Serological cross-reactions with other species showed some common epitopes of ASA110 and ASA25 present in A. porrum, A. ascalonicum, Narcissus alba, PHA and Con A but not in A. cepa. ASA110 with CHO cells indicated it to be weakly cytotoxic with LD50 of 160 microg/ml.

Amino Acids↗
PubMed1998

Regulation of proteoglycan and hyaluronan synthesis by elevated level of intracellular cyclic adenosine monophosphate in peritubular cells from immature rat testis.

The effects of an increase in intracellular cAMP concentration on proteoglycan (PG) synthesis by peritubular (PT) cells from immature rat testis were investigated. In the presence of dBcAMP for 72 h, the [3H]-hexosamine incorporation in secreted PG and in cell-associated PG was reduced, whereas [35S]-sulfate radioactivity was enhanced in secreted PG and not affected in cell-associated PG. Cholera toxin and IBMX, known to generate high intracellular cAMP levels, induced similar changes. Cyclic AMP did not alter PG protein moiety synthesis but enhanced PG turnover. Cholera toxin and dBcAMP profoundly modified PG characteristics: (1) Apparent molecular weight of PG was increased. (2) This was due to an increase in glycosaminoglycans (heparan sulfate (HS) and chondroitin sulfate (CS)) length. (3) The number of glycosaminoglycan chains was presumably reduced. (4) Heparan sulfate and chondroitin sulfate chains of medium and cell layer-associated PG appeared oversulfated. (5) The pattern of cell layer associated PG was modified with a decrease in HSPG and a correlative increase in CSPG. Cholera toxin and dBcAMP also dramatically stimulated hyaluronan synthesis by possible phosphorylation induced activation of hyaluronan synthase(s).

1-Methyl-3-isobutylxanthine↗
PubMed2001

Regulation of leptin production.

Fat mass is the primary determinant of serum leptin in humans with energy intake and gender also having significant effects. Gender influences leptin production through the reproductive hormones. Glucose metabolism links food intake to leptin production and hexosamine biosynthesis appears to play a significant role in this process. Catecholamines inhibit leptin production and the sympathetic nervous system has been proposed to be the efferent arm of the leptin signal transduction pathway between adipose tissue and the central nervous system. Additional regulators of leptin production include glucocorticoids, cytokines and agonists of PPAR gamma. In addition to adipose tissue, leptin is produced in several other places including placenta, bone marrow, stomach, muscle and perhaps brain, thus increasing the number of potential regulatory roles for this hormone. Future work will be needed to fully elucidate the mechanisms regulating leptin synthesis/release in each tissue as well as its regulatory functions.

Adipose Tissue↗
PubMed1997

Assessment of glycosaminoglycan-protein linkage tetrasaccharides as acceptors for GalNAc- and GlcNAc-transferases from mouse mastocytoma.

Two glycosaminoglycan-protein linkage tetrasaccharide-serine compounds, GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser and GlcAbeta1-3Gal(4-O-sulfate)beta1-3Galbeta1-4Xylbeta1-O -Ser, were tested as hexosamine acceptors, using UDP-[3H]GlcNAc and UDP-[3H]GalNAc as sugar donors, and solubilized mouse mastocytoma microsomes as enzyme source. The nonsulfated Ser-tetrasaccharide was found to function as an acceptor for a GalNAc residue, whereas the Ser-tetrasaccharide containing a sulfated galactose unit was inactive. Characterization of the radio-labelled product by digestion with alpha-N-acetylgalactosaminidase and beta-N-acetylhexosaminidase revealed that the [3H]GalNAc unit was alpha-linked, as in the product previously synthesized using serum enzymes, and not beta-linked as found in the chondroitin sulfate polymer. Heparan sulfate/heparin biosynthesis could not be primed by either of the two linkage Ser-tetrasaccharides, since no transfer of [3H]GlcNAc from UDP-[3H]GlcNAc could be detected. By contrast, transfer of a [3H]GlcNAc unit to a [GlcAbeta1-4GlcNAcalpha1-4]2-GlcAbeta1-4-aMan hexasaccharide acceptor used to assay the GlcNAc transferase involved in chain elongation, was readily detected. These results are in agreement with the recent proposal that two different N-acetylglucosaminyl transferases catalyse the biosynthesis of heparan sulfate. Although the mastocytoma system contains both the heparan sulfate/heparin and chondroitin sulfate biosynthetic enzymes the Ser-tetrasaccharides do not seem to fulfil the requirements to serve as acceptors for the first HexNAc transfer reactions involved in the formation of these polysaccharides.

Animals↗
PubMed2002

Cationic glycosphingolipids in neuronal tissues and their possible biological significance.

During the course of studies on natural occurrence of sphingosine base in brain, cationic glycosphingolipids bound to carboxymethyl-Sephadex and eluted with triethylamine in organic solvents were isolated and characterized. Four classes of compounds were identified: (i) plasmalopsychosine-A and -B; (ii) glyceroplasmalopsychosine; (iii) glycosphingolipids having de-N-acetyl-hexosamine, e.g., de-N-acetyl-Lc3Cer; (iv) glycosylsphingosine, i.e., lysoglycosphingolipid. Only two kinds, galactosylsphingosine (psychosine) and lactosylsphingosine, were found to occur naturally in brain. All these compounds were isolated from extract of brain white matter. Their occurrence, quantity, and distribution pattern differ from one species to another. Their quantity is much lower than that of regular acidic and neutral glycosphingolipids. They may interact with regular glycosphingolipids in glycosphingolipid-enriched microdomains to elicit signal transduction, to modify cellular phenotype, although studies along this line are highly limited at this time.

Carbohydrate Conformation↗
PubMed2002

Effect of piperine on the inhibition of lung metastasis induced B16F-10 melanoma cells in mice.

The effect of piperine on the inhibition of lung metastasis induced by B16F-10 melanoma cells was studied in C57BL/6 mice. Simultaneous administration of the compound with tumor induction produced a significant reduction (95.2%) in tumor nodule formation. Increased lung collagen hydroxyproline (22.37 microg/mg protein) in the metastasized lungs of the control animals compared to normal animals (0.95 microg/mg protein) was significantly reduced (2.59 microg/mg protein) in the piperine-treated animals. The high amount of uronic acid (355.83 microg/100 mg tissue) in the metastasized control animals was significantly reduced (65 microg/100 mg tissue) in the animals treated with piperine. Lung hexosamine content was also significantly reduced in the piperine-treated animals (0.98 mg/100 mg lyophilized tissue) compared to the untreated tumor-bearing animals (4.2 mg/100 mg lyophilized tissue). The elevated levels of serum sialic acid and serum gamma glutamyl transpeptidase activity in the untreated control animals was significantly reduced in the animals treated with piperine. The piperine-treated animals even survived the experiment (90 days). Histopathology of the lung tissue also correlated with the lifespan of the drug-treated animals. Our results demonstrate the antimetastatic activity of piperine, an alkaloid present in plants such as Piper nigrum and Piper longum.

Alkaloids↗
PubMed2004

Ganglioside/glycosphingolipid turnover: new concepts.

In this review focus is given to the metabolic turnover of gangliosides/glycosphingolipids. The metabolism and accompanying intracellular trafficking of gangliosides/glycosphingolipids is illustrated with particular attention to the following events: (a) the de novo biosynthesis in the endoplasmic reticulum and Golgi apparatus, followed by vesicular sorting to the plasma membrane; (b) the enzyme-assisted chemical modifications occurring at the plasma membrane level; (c) the internalization via endocytosis and recycling to the plasma membrane; (d) the direct glycosylations taking place after sorting from endosomes to the Golgi apparatus; (e) the degradation at the late endosomal/lysosomal level with formation of fragments of sugar (glucose, galactose, hexosamine, sialic acid) and lipid (ceramide, sphingosine, fatty acid) nature; (f) the metabolic recycling of these fragments for biosynthetic purposes (salvage pathways); and (g) further degradation of fragments to waste products. Noteworthy, the correct course of ganglioside/glycosphingolipid metabolism requires the presence of the vimentin intracellular filament net work, likely to assist intracellular transport of sphingoid molecules. ut of the above events those that can be quantitatively evaluated with acceptable reliability are the processes of de novo biosynthesis, metabolic salvage and direct glycosylation. Depending on the cultured cells employed, the percentage of distribution of de novo biosynthesis, salvage pathways, and direct glycosylation, over total metabolism were reported to be: 35% (range: 10-90%) for de novo biosynthesis, 7% (range: 5-10%) for direct glycosylation, and 58% (range: 10-90%) for salvage pathways. The attempts made to calculate the half-life of overall ganglioside turnover provided data of unsure reliability, especially because in many studies salvage pathways were not taken into consideration. The values of half-life range from 2 to 6.5 h to 3 days depending on the cells used. Available evidence for changes of ganglioside/glycosphingolipid turnover, due to extracellular stimuli, is also considered and discussed.

Animals↗
PubMed1976

Plasma membrane associated enzymes of mammary tumours as the biochemical indicators of metastasizing capacity. Analyses of enriched plasma membrane preparations.

Plasma membranes from 6 spontaneously metastasizing and 4 non-metastasizing rat mammary carcinomata were isolated by discontinuous sucrose density gradient centrifugation of microsomal pellets. The starting microsomal fraction contained 40-50% plasma membranes as determined by the levels of 5'-nucleotidase activity, with a negligible amount of nuclear (1%), mitochondrial (5%) and lysomal (7%) contamination. Five distinct fractions (F1-F5) were banded at densities 1 X 09, 1 X 13, 1 X 15, 1 X 17 and 1 X 21 at 25 degrees C, in addition to a pellet (F6) obtained by centrifuging at 76,000 g for 17 h. The fractions F1 through F5, all contained various concentrations of membranous structures, while the pellet (F6) contained only amorphous materials as evidenced by electron microscopy. The F3 fraction at the gradient 1 X 15 had the highest specific as well as total activity of the plasma membrane marker enzyme, with aggregates of the least contaminated plasma membranes in vesicular forms. This fraction also had the lowest specific activity for glucose-6-phosphatase (smooth ER marker) and for beta-D-glucuronidase (lysomal marker), and therefore was considered to be the "cleanest" plasma membrane fraction. When the activity of 4 additional plasma membrane marker enzymes, i.e., alkaline phosphatase, phosphodiesterase I, nucleotide pyrophosphatase and alkaline ribonuclease was determined in the same F3 fraction, their levels were significantly lower in every metastasizing tumour than in the non-metastasizing ones, with the enzyme activity decreasing in direct proportion to the metastasizing capacity. On the other hand, the marker enzymes were high in all non-metastasizing tumours, with the activity seemingly increasing with the immunogenicity of tumour cells. There was no significant difference between the 2 groups of mammary tumours in the levels of sialic acid, hexosamine, phospholipid or cholesterol in the plasma membranes. Thus, the level of plasma membrane marker enzymes is considered an accurate indicator for metastasizing capacity in the rat mammary tumour system.

Alkaline Phosphatase↗
PubMed2005

O-GlcNAc modification on IRS-1 and Akt2 by PUGNAc inhibits their phosphorylation and induces insulin resistance in rat primary adipocytes.

It has been known that O-linked beta-N-acetylglucosamine (O-GlcNAc) modification of proteins plays an important role in transcription, translation, nuclear transport and signal transduction. The increased flux of glucose through the hexosamine biosynthetic pathway (HBP) and increased O-GlcNAc modification of protein have been suggested as one of the causes in the development of insulin resistance. However, it is not clear at the molecular level, how O-GlcNAc protein modification results in substantial impairment of insulin signaling. To clarify the association of O-GlcNAc protein modification and insulin resistance in rat primary adipocytes, we treated the adipocytes with O-(2-acetamido-2deoxy-D-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc), a potent inhibitor of O-GlcNAcase that catalyzes removal of O-GlcNAc from proteins. Prolonged treatment of PUGNAc (100 microM for 12 h) increased O-GlcNAc modification on proteins in adipocytes. PUGNAc also drastically decreased insulin-stimulated 2-deoxyglucose (2DG) uptake and GLUT4 translocation in adipocytes, indicating that PUGNAc developed impaired glucose utilization and insulin resistance in adipocytes. Interestingly, the O-GlcNAc modification of IRS-1 and Akt2 was increased by PUGNAc, accompanied by a partial reduction of insulin-stimulated phosphorylations of IRS-1 and Akt2. The PUGNAc treatment has no effect on the expression level of GLUT4, whereas O-GlcNAc modification of GLUT4 was increased. These results suggest that the increase of O-GlcNAc modification on insulin signal pathway intermediates, such as IRS-1 and Akt2, reduces the insulin-stimulated phosphorylation of IRS-1 and Akt2, subsequently leading to insulin resistance in rat primary adipocytes.

Acetylglucosamine↗