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At least 919 records · Page 51Linked to original sources
PubMed1981

Structural gene products of the murine Ah complex. Differences in ontogenesis and glucosamine incorporation between liver microsomal cytochromes P1-450 and P-448 induced by polycyclic aromatic compounds.

Antibodies against mouse-liver microsomal cytochromes P1-450 and P-448, two polycyclic aromatic inducible cytochromes, were previously developed [Negishi, M. and Nebert, D.W. (1979) J. Biol. Chem. 254, 11015-11023]. Liver microsomes from 3-methylcholanthrene-treated and phenobarbital-treated and control adult mice and 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated adult and fetal mice were examined. Immunoprecipitable radioactivity was measured, following labeling with pyridoxal phosphate/NaB[3H]4 or with 125I-labeled p-aminosulfobenzoic acid/NaNO2 in vitro or with [3H]leucine, [14C]glucosamine, or [32P]O4 in vivo. (a) Induction of cytochrome P1-450 occurs developmentally earlier in gestation than induction of cytochrome P-448 when the mother is treated with polycyclic aromatic compounds. (b) There appears to be a basal form of cytochrome P-448 but no cytochrome P1-450 in control liver microsomes; inducibility of cytochrome P-448 thus ranges between 5--12-fold, whereas that of P1-450 is infinite. (c) Phenobarbital pretreatment induces no detectable P1-450 or P-448. (d) P-448 appears to be either greater in concentration than P1-450 in the membrane or more exposed than P1-450 on the microsomal membrane surface. (e) By the radioimmunoassay methods used, 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced P1-450 and P-448 in Ah-nonresponsive mice are indistinguishable from those in Ah-responsive mice; this is true in both the fetus and the adult. (f) Compared with P-448 expression, the expression of P1-450 is more closely associated with 3-methylcholanthrene-induced aryl hydrocarbon hydroxylase activity, and these two structural gene products are apparently regulated independently. (g) P-448 but not P1-450 appears to be a glycoprotein. These data illustrate further differences between two forms of polycyclic aromatic-inducible P-450 in mouse liver. Neither P1-450 nor P-448 appears to be a phosphoprotein. Neither anti-(P1-450) nor anti-(P-448) precipitates any forms of liver microsomal P-450 from beta-naphthoflavone-treated adult rabbits and, conversely, anti-LM4 (the antibody to rabbit liver microsomal P-450 form 4) does not precipitate any forms of liver microsomal P-450 from 3-methylcholanthrene-treated C57BL/6N mice.

Animals↗
PubMed1981

[14C]glucosamine incorporation into intestinal glycoproteins by calf intestinal epithelium in organ culture.

The uptake and incorporation of [14C]glucosamine into secreted intestinal glycoproteins was examined in the calf intestinal mucosa and isolated epithelial cells, using an organ culture system. Incorporation varied with the area of the intestine, ie duodenum greater than jejunum greater than ileum. Secreted glycoproteins were examined after 3 and 24 hours in organ culture. Initially, a glycoprotein approximately 68,000 molecular weight (mol wt) was secreted by all areas of the intestine. This was followed by the appearance of a larger glycoprotein 10(6) to 10(7) mol wt. Enzymatic cleavage of jejunal brush borders released a glycocalyx glycoprotein similar in size to the secreted large mol wt glycoprotein. These similarities in mol wt are only suggestive evidence that the 2 large glycoproteins are the same. This procedure allows for the study of the maturation and development of a poorly understood component of the intestinal epithelial cell which has a wide range of functional considerations.

Animals↗
PubMedDate not supplied

[A study of thyroglobulin biosynthesis by the incorporation of glucosamine-14C, mannose-14C and galactose-14C in thyroid gland cell-free systems].

The authors studied in the microsomal and polyribosomal protein-synthesizing system of the thyroid gland a combination of carbohydrate components of thyroglobulin by the incorporation of labeled D-glucosamine-14C, D-mannose-14C, and galactose-14C. It was shown that in the process of protein biosynthesis there occurred in the microsomal system a combination of carbohydrate-14C; no combination of carbohydrates was noted in the polyribosomic system. Analysis of the synthesized proteins was carried out by disc-electrophoresis. All the carbohydrates under study were revealed both in the 19S molecule of thyroglobulin and in its 3-8 subunits. Thus, a combination of carbohydrate components occurred after the termination of peptide chain synthesis and already at the microsome level.

Animals↗
PubMed1998

Efficacy and safety of glucosamine sulfate versus ibuprofen in patients with knee osteoarthritis.

A double-blind therapeutic investigation was performed on 178 Chinese patients suffering from osteoarthritis of the knee randomized into two groups, one treated for 4 weeks with glucosamine sulfate (GS, CAS 29031-19-4, Viartril-S) at the daily dose of 1,500 mg and the other with ibuprofen (IBU, CAS 15687-27-1) at the daily dose of 1,200 mg. Knee pain at rest, at movement and at pressure, knee swelling, improvement and therapeutic utility as well as adverse events and drop-outs were recorded after 2 and 4 weeks of treatment. The variables were recorded also after 2 weeks of treatment discontinuation in order to appreciate the remnant therapeutic effect. Both GS and IBU significantly reduced the symptoms of osteoarthritis with the trend of GS to be more effective. After 2 weeks of drug discontinuation there was a remnant therapeutic effect in both groups, with the trend to be more pronounced in the GS group. GS was significantly better tolerated than IBU, as shown by the adverse drug reactions (6% in the patients of the GS group and 16% in the IBU group--p = 0.02) and by the drug-related drop-outs (0% of the patients in the GS group and 10% in the IBU group--p = 0.0017). The better tolerability of GS is explained by its mode of action, because GS specifically curbs the pathogenic mechanisms of osteoarthritis and does not inhibit the cyclo-oxygenases as the non-steroidal anti-inflammatory drugs (NSAIDs) do, with the consequent anti-inflammatory analgesic activities but also with the several adverse reactions due to this not targeted effect. The present study confirms that GS is a selective drug for osteoarthritis, as effective on the symptoms of the disease as NSAIDs but significantly better tolerated. For these properties GS seems particularly indicated in the long-term treatments needed in osteoarthritis.

Adult↗
PubMed1999

Alkaline biocatalysis for the direct synthesis of N-acetyl-D-neuraminic acid (Neu5Ac) from N-acetyl-D-glucosamine (GlcNAc).

Integration between the alkaline epimerization of N-acetyl-D-glucosamine (GlcNAc) to N-Acetyl-D-mannosamine (ManNAc) and the N-acetyl-D-neuraminic acid (Neu5Ac) aldolase-catalyzed biotransformation has been assessed experimentally. GlcNAc epimerization took place above pH 9.0, and the initial rate of ManNAc formation increased exponentially to 10.37 mmol/L per hour at pH 12. However, above this pH, severe degradation of pyruvate occurred. A value of 31.3% molar conversion on Pyr was achieved in an integrated biotransformation. The "pseudo"-steady state at the end of the reaction was comparable to the equilibrium achieved with a combination of an epimerase and aldolase enzymes. The integrated reaction proved feasible, but at the expense of pyruvate and Neu5Ac aldolase degradation.

Acetylglucosamine↗
PubMed1999

Human glucosamine-6-phosphate isomerase, a homologue of hamster oscillin, does not appear to be involved in Ca2+ release in mammalian oocytes.

Injections of cytosolic preparations from mammalian sperm into oocytes have been shown to trigger calcium [Ca2+]i oscillations and initiate activation of development. Recently, a protein isolated from hamster sperm has been suggested to be involved in the generation of these oscillations and it was named "oscillin." The human homologue of hamster oscillin is glucosamine 6-phosphate isomerase (GPI, EC no. 5.3.1.10), an enzyme so far described to be involved in hexose phosphate metabolism. To assess the role of GPI on Ca2+ signaling, a human recombinant protein was generated in a prokaryotic system and injected into fura-2-dextran-loaded metaphase II (MII) mouse oocytes. Injection of recombinant GPI failed to induce Ca2+ responses in 12/12 injected MII oocytes despite the fact that the recombinant GPI was active as assessed by an enzymatic assay. Injection of buffer (0/6 oocytes) or fructose-6-phosphate, a product of GPI enzymatic reaction (0/5 oocytes), also failed to initiate Ca2+ responses. Conversely, injections of sperm cytosolic factor induced [Ca2+]i oscillations in all 17/17 oocytes. In addition, injection of recombinant GPI or GPI mRNA failed to induce parthenogenetic activation (0/30 oocytes). Immunofluorescence studies using an anti-GPI polyclonal antibody (GK) resulted in localization of GPI to the sperm's equatorial region. Incubation of the GK antibody with sperm extracts failed to block the [Ca2+]i responses induced by these extracts. Moreover, near complete depletion of GPI from sperm fractions by immunoprecipitation did not impair the ability of these fractions to induce [Ca2+]i oscillations. In summary, our results support the role of a sperm cytosolic component(s) in the generation of [Ca2+]i oscillations during mammalian fertilization, although a protein other than GPI/oscillin is likely to be the active calcium releasing factor.

Aldose-Ketose Isomerases↗
PubMed2005

Arterial embolization using poly-N-acetyl glucosamine gel in a rat kidney model.

Aqueous solutions of poly-N-acetyl glucosamine (p-GlcNAc) exhibit a liquid-gel transition at physiological pH and temperature. This feature inspired the authors to conduct a study to evaluate the macro- and histological changes of rat kidneys after embolization using either p-GlcNAc gel injection into the renal artery or ligation of the renal artery. The procedures were performed in 46 rats through open abdominal surgeries. Animals were sacrificed at 3 days and at 1, 3, 5, and 8 weeks postoperatively. The results of both macro-observation and histological study showed that p-GlcNAc gels were effective in causing necrosis and subsequent fibrosis in all embolized kidneys. The data indicate that p-GlcNAc gel may have promise as an effective agent for therapeutic embolization.

Acetylglucosamine↗
PubMed1994

Oligodendrocytes produce low molecular weight glycoproteins containing N-acetyl-D-glucosamine in their Golgi apparatus.

Lectin histochemistry using the Griffonia simplicifolia II lectin (GSL II) has revealed a novel group of glycoproteins containing terminal N-acetyl-D-glucosamine (GlcNAc) residues in oligodendrocytes. The GlcNAc-containing glycoproteins were not present in other types of glial cells, but were expressed by some neuronal cell populations. Within oligodendrocytes their localization was confined to the Golgi apparatus, as determined ultrastructurally. Biochemical analyses using tricine/SDS-polyacrylamide gel electrophoresis and western blotting with GSL II showed the GlcNAc-containing glycoproteins to be insoluble, with molecular masses ranging from 15 to 30 kDa. Our study provides a first account of insoluble, GlcNAc-rich 15-30 kDa glycoproteins in oligodendroglia. The findings are discussed in the context of the functional significance of other known oligodendrocyte glycoproteins.

Acetylglucosamine↗
PubMed2003

Cloning and functional characterization of GNPI2, a novel human homolog of glucosamine-6-phosphate isomerase/oscillin.

The enzyme, glucosamine-6-phosphate isomerase (GNPI) or deaminase (GNPDA) (EC 5.3.1.10), catalyzes the conversion of GNP to fructose-6-phosphate and ammonia, with an aldo/keto isomerization and an amination/deamination. A hamster sperm-derived protein (Oscillin) with high similarity to bacterial GNPI has been proved to be capable of inducing calcium oscillation in eggs at fertilization. GNPI/Oscillin was supposed to be an important factor in starting embryonic development. From the cDNA library of human dendritic cells (DC), we isolated a novel full-length cDNA encoding a 276-amino acid-residue protein that shares high homology with human GNPI/Oscillin. So, the novel molecule is named as GNPI2. The GNPI2 gene consists of seven exons and six introns. It is mapped to chromosome 4. Northern blot analysis indicated that the tissue distribution of GNPI2 mRNA is different from that of human GNPI or Oscillin mRNA. GNPI2 is ubiquitously expressed in most of human tissues with high expression in testis, ovary, placenta, and heart. Like GNPI, the recombinant GNPI2 has been proved to have the enzymatic activity to catalyze the conversion of GNP to fructose-6-phosphate. Our results indicated that GNPI2 is a novel protein with definite function as a GNPI.

Aldose-Ketose Isomerases↗
PubMed2001

An improved assay for the N-acetyl-D-glucosamine reducing ends of polysaccharides in the presence of proteins.

Hyaluronan concentration and hyaluronidase activity can be assayed by using different techniques including turbidimetry, viscosimetry, ELISA, chromatography, and colorimetry. The most popular colorimetric method is that of J. Reissig et al. (1955, J. Biol. Chem. 217, 959-966), in which the color results from a reaction between the Ehrlich's reagent (DMAB) and the N-acetyl-d-glucosamine reducing end of each hyaluronan chain. Nevertheless, there are problems with this method when proteins are present in the medium. Here we propose a new interpretation of the Reissig signal for estimating such reducing ends in media containing enzymes or other proteins. This interpretation is based on the fact that the absorbance obtained by using the Reissig method results from two factors: a turbidity due to the formation of polysaccharide-protein complexes and a color resulting from the action of DMAB on the reducing end of the polysaccharide chains. The turbidity at 585 nm, the wavelength at which the color intensity is maximal, may be estimated by curve fitting the spectrum between 450 and 650 nm. Subtracting the turbidity from the absorbance gives the colorimetric intensity which represents the concentration of polysaccharide chains. Moreover, the turbidity may give additional information about the existence of polysaccharide-protein complexes and their nature.

Acetylglucosamine↗
PubMed2001

Use of galactosyltransferase to assess the biological function of O-linked N-acetyl-d-glucosamine: a potential role for O-GlcNAc during cell division.

Many cytosolic and nuclear proteins are modified by monomeric O-linked N-acetyl-d-glucosamine (O-GlcNAc). The biological functions of this form of glycosylation are unclear but evidence suggests that it heightens regulation of protein function. To assess the biological function of O-GlcNAc addition, we examined the biological effects of galactosyltransferase (GalT) microinjected into the cytoplasm of Xenopus ovarian oocytes. GalT, which catalyzes beta1-4-galactose addition to O-GlcNAc, should inhibit deglycosylation and lectin-like interactions requiring unmodified O-GlcNAc residues. Although GalT injection into diplotene-arrested oocytes has no detectable effects on cell viability, it is toxic to oocytes entering meiosis. Cell-cycle-specific toxicity is recapitulated in vitro as GalT inhibits formation of nuclei and microtubule asters from cell-free extracts of ovulated frog eggs. These observations suggest that regulation of O-GlcNAc is important for cell cycle progression and may be important in diseases in which O-GlcNAc metabolism is abnormal. The methods described here outline a viable experimental scheme for ascribing a biological function to this form of glycosylation.

Acetylglucosamine↗
PubMed1994

Crystallization and preliminary X-ray analysis of the two domains of glucosamine-6-phosphate synthase from Escherichia coli.

The glutamine amidohydrolase and fructose 6-phosphate binding domains of glucosamine-6-phosphate synthase from Escherichia coli have been overexpressed, purified and crystallized for X-ray diffraction analysis. The crystals of the glutamine amidohydrolase domain belong to the orthorhombic space group P2(1)2(1)2(1) with cell dimensions a = 70.4 A, b = 82.5 A, c = 86.1 A, with two molecules in the asymmetric unit, and diffract to 1.9 A resolution. The native Patterson indicated pseudo c-face centering of the unit cell. The fructose 6-phosphate binding domain was crystallized in the hexagonal space group P6(1) or P6(5) with cell dimensions a = b = 63.5 A, c = 334.3 A and with two molecules in the asymmetric unit. Diffraction data to 2.6 A resolution have been collected.

Binding Sites↗
PubMed2000

On the role of the N-terminal group in the allosteric function of glucosamine-6-phosphate deaminase from Escherichia coli.

Glucosamine-6-phosphate deaminase (EC 3.5.99.6) from Escherichia coli is an allosteric enzyme of the K-type, activated by N-acetylglucosamine 6-phosphate. It is a homohexamer and has six allosteric sites located in clefts between the subunits. The amino acid side-chains in the allosteric site involved in phosphate binding are Arg158, Lys160 and Ser151 from one subunit and the N-terminal amino group from the facing polypeptide chain. To study the functional role of the terminal amino group, we utilized a specific non-enzymic transamination reaction, and we further reduced the product with borohydride, to obtain the corresponding enzyme with a terminal hydroxy group. Several experimental controls were performed to assess the procedure, including reconditioning of the enzyme samples by refolding chromatography. Allosteric activation by N-acetylglucosamine 6-phosphate became of the K-V mixed type in the transaminated protein. Its kinetic study suggests that the allosteric equilibrium for this modified enzyme is displaced to the R state, with the consequent loss of co-operativity. The deaminase with a terminal hydroxy acid, obtained by reducing the transaminated enzyme, showed significant recovery of the catalytic activity and its allosteric activation pattern became similar to that found for the unmodified enzyme. It had lost, however, the pH-dependence of homotropic co-operativity shown by the unmodified deaminase in the pH range 6-8. These results show that the terminal amino group plays a part in the co-operativity of the enzyme and, more importantly, indicate that the loss of this co- operativity at low pH is due to the hydronation of this amino group.

Acetylglucosamine↗
PubMed2000

Purification to homogeneity of Candida albicans glucosamine-6-phosphate synthase overexpressed in Escherichia coli.

The Candida albicans GFA1 gene encoding glucosamine-6-phosphate synthase, an enzyme of cell wall biosynthesis pathway in fungi and bacteria, recently an object of interest as a target for the chemotherapy of systemic mycoses, was PCR amplified and cloned to an Escherichia coli expression vector pET23b. The activity of the enzyme in the lysates from the overproducing E. coli strain was approximately 50-100 times higher than in the lysates from the control E. coli strain. This abundant overproduction allows to purify milligram amounts of the enzyme to homogeneity.

Candida albicans↗
PubMed1992

Investigation of the inhibition pathway of glucosamine synthase by N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid by semiempirical quantum mechanical and molecular mechanics methods.

Glucosamine synthase (E.C. 2.6.1.16) is a promising target in antifungal drug design. It has been reported that its potent inhibitor, N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP), inactivates the enzyme by the Michael addition of the S-H group to the FMDP molecule followed by cyclisation reactions. In this study we have investigated, by means of semiempirical MNDO, PM3 and molecular mechanics methods, the energetics and kinetic possibility of the formation of various stereoisomers of the products of cyclisation of the Michael addition products detected experimentally. It was found that the substituted 1,4-thiazin-3-one can be formed in one step under alkaline conditions; the stereoisomers of this compound predicted to be the most stable on the basis of theoretical calculations are also the dominant ones in reality.

Calorimetry↗
PubMed1992

A theoretical study of glucosamine synthase. II. Combined quantum and molecular mechanics simulation of sulfhydryl attack on the carboxyamide group.

Continuing our theoretical studies of glucosamine synthase catalysis, we have carried out MNDO and ab initio calculations of the first stage of the reaction, which involves the attack of a cysteine thiol group from the enzyme active site on the side chain carboxyamide group of glutamine, producing ammonia and thioester. The reactants were modelled by methyl mercaptate and acetamide, respectively. For two considered mechanisms of the reaction the energy surfaces were evaluated. Mechanism I, proposed by Chmara et al. (1985) involves the nucleophilic attack of a deprotonated thiol group on the carbonyl carbon atom. Mechanism II, postulated in our previous work (Tempczyk et al. 1989), assumes the concerted binding of the mercaptate sulphur to the carbonyl carbon and the sulfhydryl hydrogen to the amide nitrogen with simultaneous breaking of the S-H bond. The energy surface of mechanism I shows no minimum on the approach of the mercaptide anion towards the carbonyl carbon, which is also consistent with ab initio calculations in a 4-31 G basis set. Therefore, mechanism I seems to be unlikely. The same analysis of mechanism II shows that it leads to the desired products: methyl thioacetate and ammonia. The presence of a sulfhydryl hydrogen causes apparent pyramidicity of the amido nitrogen and lengthening of the C-N bond in the transition state, making conditions for the release of the ammonia molecule. The MNDO calculated energy barrier of the reaction is 50.1 kcal/mol and the approximate 4-31 G ab initio barrier (at the MNDO geometries of the substrate complex and the transition state) is 63 kcal/mol.(ABSTRACT TRUNCATED AT 250 WORDS)

Amides↗