Biomedical subjects

R Tauber

Publications and source records attributed to R Tauber.

At least 19 recordsLinked to original sources

PubMed1992

Biosynthesis and metabolism of dipeptidylpeptidase IV in primary cultured rat hepatocytes and Morris hepatoma 7777 cells.

N-Glycosylation, biosynthesis and degradation of dipeptidylpeptidase IV (EC 3.4.14.5) (DPP IV) were comparatively studied in primary cultured rat hepatocytes and Morris hepatoma 7777 cells (MH 7777 cells). DPP IV had a molecular mass of 105 kDa in rat hepatocytes and of 103 kDa in MH 7777 cells as assessed by SDS/PAGE under reducing conditions. This difference in molecular mass was caused by differences in covalently attached N-glycans. DPP IV from hepatoma cells contained a higher proportion of N-glycans of the oligomannosidic or hybrid type and therefore migrated at a slightly lower molecular mass. In both cell types DPP IV was initially synthesized as a 97-kDa precursor which was completely susceptible to digestion with endo-beta-N-acetylglucosaminidase H converting the molecular mass to 84 kDa. The precursor was processed to the mature forms of DPP IV, glycosylated with N-glycans mainly of the complex type with a half-life of 20-25 min. The transit of newly synthesized DPP IV to the cell surface displayed identical or very similar kinetics in both cell types with the major portion of DPP IV appearing at the cell surface after 60 min. DPP IV molecules were very slowly degraded in hepatocytes as well as in hepatoma cells with half-lives of approximately 45 h. Inhibition of oligosaccharide processing with 1-deoxymannojirimycin led to the formation of DPP IV molecules containing N-glycans of the oligomannosidic type. This glycosylation variant was degraded with the same half-life as complex-type glycosylated DPP IV. By contrast, inhibition of N-glycosylation with tunicamycin resulted into rapid degradation of non-N-glycosylated DPP IV molecules in both cell types. Non-N-glycosylated DPP IV could not be detected at the cell surface indicating an intracellular proteolytic process soon after biosynthesis.

Animals↗

PubMed1992

Lectin specificity and binding characteristics of human C-reactive protein.

C-reactive protein (CRP) is thought to play an important role in immunomodulation. The exact biologic function of this pentraxin protein is, however, still unclear. Here we report experiments designed to further characterize the binding properties of CRP. Using purified human CRP it could be shown that CRP immobilized onto polystyrene surfaces or onto latex beads binds distinct plasma glycoproteins including IgG, asialofetuin, asialo-beta 2-glycoprotein I and, likewise, synthetic glycoproteins as a lectin, exhibiting binding specificity for terminal galactosyl residues of the glycoprotein glycans. Binding of CRP to IgA, IgM, IgG, asialofetuin, asialo-beta 2-glycoprotein I and to synthetic glycoproteins requires immobilization onto surfaces of both CRP and the ligand. Fibronectin and fibrinogen are bound by surface-immobilized CRP also in soluble phase. Comparing various mono-, di-, and trisaccharides as competitive inhibitors of the lectin binding activity of CRP, only beta-D-Gal-(1-3)-D-GalNAc, beta-D-Gal-(1-4)-D-GalNAc, and beta-D-Gal-(1-4)-beta-D-Gal-(1-4)-D-GlcNAc had significant inhibitory power at a concentration of 8 mmol/liter. Binding activity of CRP was pH-dependent with an optimum at pH 5 to 6 and was reduced by 90% when pH was shifted from 6 to the physiologic pH value of 7.4. CRP exhibited lectin-like properties with binding specificity for galactosyl residues also when bound to K-562 erythroleukemia cells. It is therefore suggested that CRP immobilized onto surfaces exhibits lectin activity toward galactosyl groups preferentially in a mildly acidic environment as present at sites of inflammation.

Blood Proteins↗

PubMed1992

Structure of the N-linked oligosaccharides of the human transferrin receptor.

Human transferrin receptor was isolated from placenta and from the hepatocarcinoma cell line Hep G2. Asparagine-linked oligosaccharides were released by treatment of tryptic glycopeptides with endo-beta-N-acetylglucosaminidase H or peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Oligosaccharide alditols were fractionated by anion-exchange high-performance liquid chromatography and by high-pH anion-exchange chromatography. Glycans from placental transferrin receptor were further characterized, after desialylation, by methylation analysis and, in part, by liquid secondary-ion mass spectrometry. Sialylation of placental transferrin receptor was examined by lectin affinity blotting with Sambucus nigra agglutinin and Maackia amurensis agglutinin. In order to trace possible inter-individual differences in N-glycosylation of the receptor, two preparations of placental transferrin receptor purified from two donors were compared. The results demonstrate that human transferrin receptor from placenta predominantly carries diantennary and triantennary N-acetyllactosaminic glycans as well as hybrid-type species, the galactose residues of which being almost completely substituted with (alpha 2-3)-linked sialic acid residues. Distinct differences were noted in the glycosylation pattern of the receptor from different individuals. Transferrin receptor from donor A carried predominantly diantennary and triantennary complex-type glycans, in part fucosylated at the innermost N-acetylglucosamine residue, in addition to small amounts of bisected and of incomplete diantennary species. Placental transferrin receptor from donor B predominantly carried triantennary N-acetyllactosaminic glycans without fucose and hybrid-type oligosaccharides with four or five mannose residues. Distinct from placental transferrin receptor, the receptor from Hep G2 cells contained larger amounts of oligomannosidic glycans with six to nine mannose residues and tetrasialylated complex-type oligosaccharides apart from mono-, di- and trisialylated species.

Agglutinins↗

PubMed1992

N-glycosylation of membrane glycoproteins in retinol-deficient rat liver.

The effect of vitamin A deficiency on N-linked oligosaccharides of membrane glycoproteins was studied in rat liver in order to evaluate the suggested role of retinol in protein N-glycosylation. First, oligosaccharides of newly synthesized glycoproteins from rough endoplasmic reticulum of vitamin A deficient liver were compared with that of pair-fed controls. Oligosaccharides were metabolically labelled with D-[2-3H]mannose, released from the glycoproteins with endoglycosidase H, purified by reversed phase HPLC and ion exchange chromatography, and were reduced with sodium borohydride. HPLC fractionation of the oligosaccharide alditols showed that the glycoproteins carried mainly four oligosaccharide species, Glc1Man9GlcNAc2, Man9GlcNAc2, Man8GlcNAc2 and Man7GlcNAc2, in identical relative amounts in the vitamin A deficient and the control tissue. In particular, no increase in the proportion of short chain oligosaccharides was noted in vitamin A deficient liver. Second, the number of N-linked oligosaccharides was estimated in dipeptidylpeptidase IV (DPP IV), a major glycoprotein constituent of the hepatic plasma membrane, comparing the newly synthesized glycoprotein from rough endoplasmic reticulum and the mature form of DPP IV from the plasma membrane. No evidence was obtained that retinol deficiency caused incomplete glycosylation of this membrane glycoprotein. From these data, the suggested role of retinol as a cofactor involved in the synthesis of N-linked oligosaccharides of glycoproteins must be questioned.

Animals↗

PubMed1991

2-Deoxy-2-fluoro-D-galactose protein N-glycosylation.

2-Deoxy-2-fluoro-D-galactose (dGalF), added to the medium of primary cultured rat hepatocytes, inhibited N-glycosylation of membrane (gp 120) and secretory glycoproteins (alpha 1-macroglobulin) in a concentration-dependent manner. Complete inhibition of N-glycosylation was achieved at concentrations of 1 mM and above. At identical concentrations, 2-deoxy-2-fluoro-D-glucose (dGlcF) caused only incomplete inhibition of N-glycosylation. dGalF reduced incorporation of D-[2,6-3H]mannose into lipid-linked oligosaccharides indicating interference with their assembly in the dolichol cycle.

Animals↗

PubMed1991

Portacaval shunt as an experimental model of impaired hepatic release of vitamin A in liver disease.

Vitamin A concentrations in serum and liver were studied in rats with a portacaval shunt for 48 days after shunt surgery. In addition, serum and tissue concentrations of zinc were analyzed. Following portacaval shunting serum vitamin A concentration decreased to 25% of the level in sham-operated controls, whereas serum zinc concentration decreased to 80%. The mean urinary excretion rate of zinc increased in shunted rats [18.7 +/- 2.1 micrograms/day (0.28 +/- 0.03 mumol/day)] compared with controls [13.8 +/- 1.7 micrograms/day (0.21 +/- 0.03 mumol/day)] (P less than 0.01). The concentration of retinol and total retinoids in liver tissue increased 2-3-fold in rats with a portacaval shunt, and the ratio of retinol to retinoids was slightly increased. The differences were reduced when the total organ content was calculated, because of the reduced liver weight in the shunted rats. The concentration of zinc in liver tissue decreased in rats with portacaval shunts [30.8 +/- 4.9 micrograms/g wet wt (0.47 +/- 0.07 mumol/g) vs. 35.6 +/- 3.7 micrograms/g wet wt (0.54 +/- 0.06 mumol/g) in controls; P less than 0.01]. The concentration of zinc was inversely correlated with retinol (r = -0.52, P less than 0.05) and total retinoid levels (r = -0.70, P less than 0.05) in rats with portacaval shunts but not in controls. The data are consistent with the hypothesis of an impaired release of vitamin A from the liver in rats with portacaval shunts, an impairment that could be due to liver zinc deficiency.

Animals↗

PubMed1990

Glycoproteins of rat liver plasma membranes: their hepatocellular, intestinal and renal expression in rat, rabbit and human.

Expression of six glycoproteins (Mr = 60,000 (gp 60), 80,000 (gp 80), 110,000 (gp 110), 120,000 (gp 120), 140,000 (gp 140), 160,000 (gp 160)) recently purified from rat liver plasma membranes (LPM) were compared in the liver, small intestine and kidney of the rat, rabbit and human. Immunoblotting studies with monospecific antisera showed that five of the six glycoproteins (gp 60, gp 80, gp 110, gp 120, and gp 140) were expressed not only in LPM of the rat but also in LPM from the rabbit and human with Mr corresponding to those of the glycoproteins isolated from the rat. In contrast, the glycoprotein gp 160 was only detected in rat liver. The same pattern of expression was found by immunofluorescence on isolated hepatocytes from the three species. In rat liver, the glycoproteins were localized primarily either in the bile canalicular domain (gp 80, gp 110, gp 120), or in the sinusoidal domain (gp 60, gp 140), or they were distributed over the whole hepatocellular surface (gp 160). In rat, but not in rabbit or human, the glycoproteins gp 110, gp 120 and gp 140 were also found in the small intestine localized either in the brush border membrane (gp 110, gp 120) or over the whole surface membrane of enterocytes (gp 140). Gp 120 was also detected in the luminal pole of tubular epithelial cells of rats kidney. The data show that LPM of different mammalian species share several common glycoprotein antigens. These glycoproteins, that are also partly expressed in extrahepatic tissues, may represent plasma membrane structures conserved among mammalian species.

Animals↗

PubMed1989

Rapid intramolecular turnover of N-linked glycans in plasma membrane glycoproteins. Extension of intramolecular turnover to the core sugars in plasma membrane glycoproteins of hepatoma.

Plasma membrane glycoproteins of rat hepatocytes undergo a rapid terminal deglycosylation in that the terminal sugars of the oligosaccharide side chains are rapidly removed from the otherwise intact glycoproteins [Tauber, R., Park, C.S. & Reutter, W. (1983) Proc. Natl Acad. Sci. USA 80, 4026-4029]. The present paper demonstrates that this rapid intramolecular turnover of plasma membrane glycoproteins is not restricted to peripheral sugars but, in contrast to liver, in hepatoma the core sugars of the oligosaccharide chains are also involved. Intramolecular turnover was measured in Morris hepatoma 7777 in five plasma membrane glycoproteins with Mr of 85,000 (hgp85), 105,000 (hgp105), 115,000 (hgp115), 125,000 (hgp125), 175,000 (hgp175) (hgp = hepatoma glycoprotein) that were isolated and purified to homogeneity by concanavalin-A--Sepharose affinity chromatography and semipreparative SDS gel electrophoresis. Analysis of the carbohydrates of hgp85, hgp105, hgp115 and hgp125 revealed the presence of N-linked oligosaccharides containing L-fucose, D-galactose, D-mannose and N-acetyl-D-glucosamine, but only of trace amounts of N-acetyl-D-galactosamine; hgp175 additionally contained significant amounts of N-acetyl-D-galactosamine, indicating the presence of both N- and O-linked oligosaccharides. As shown by digestion with endoglucosaminidase H, the N-linked oligosaccharides of hgp105, hgp115, hgp125 and hgp175 were of the complex type, whereas hgp85 also contained oligosaccharides of the high-mannose type. Half-lives of the turnover of the oligosacharide chains and of the protein backbone of the five glycoproteins were measured in the plasma membrane in pulse-chase experiments in vivo, using L-[3H]fucose as a marker of terminal sugars, D-[3H]mannose as marker of a core sugar and L-[3H]leucine for labelling the protein backbone. Protein backbones of the five glycoproteins were degraded with individual half-lives ranging over 41-90 h with a mean of 66 h. Compared to the degradation of the polypeptide backbone, both the terminal sugar L-fucose and the core sugar D-mannose turned over with much shorter half-lives averaging about 20 h in the five glycoproteins. The data show that, conversely to liver, within plasma membrane glycoproteins of hepatoma not only peripheral sugars but also core sugars of the oligosaccharides are split off during the life-span of the protein backbone. It may therefore be assumed that this reprocessing of plasma membrane glycoproteins is sensitive to malignant transformation.

Animals↗

PubMed1989

Decreased intramolecular turnover of L-fucose in membrane glycoproteins of rat liver during liver regeneration.

In plasma membrane glycoproteins of rat liver L-fucose undergoes a rapid intramolecular turnover in that fucose residues are removed from the glycoproteins (Tauber, R., Park, C.S. & Reutter, W. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 4026-4029). The present paper demonstrates that the intramolecular turnover of L-fucose is markedly decreased during liver regeneration. Turnover half-lives of L-fucose were measured in regenerating liver by pulse-chase experiments in five plasma membrane glycoproteins (Mr 60,000 (gp60), 80,000 (gp80), 120,000 (gp120), 140,000 (gp140), and 160,000 (gp160). The glycoproteins were isolated from plasma membranes by concanavalin A-Sepharose affinity chromatography and semipreparative NaDodSO4 polyacrylamide gel electrophoresis. L-Fucose turned over in the five glycoproteins with heterogeneous half-lives ranging from 22 h (gp160) to 49 h (gp120). The protein moieties of the glycoproteins were degraded with half-lives ranging from 56 h (gp80) to 107 h (gp140). Relative to the half-life of the protein backbone the half-live of L-fucose was increased in the five membrane glycoproteins by 70% (gp60), 150% (gp80), 182% (gp120), 60% (gp140) and 16% (gp160) during liver regeneration when compared to normal liver. The data show that L-fucose turns over in different membrane glycoproteins with individual rates, and that loss of L-fucose from plasma membrane glycoproteins is reduced in rapidly proliferating liver after partial hepatectomy.

Animals↗

PubMed1989

Developmental changes in the glycosylation and binding properties of human fibronectins. Characterization of the glycan structures and ligand binding of human fibronectins from adult plasma, cord blood and amniotic fluid.

Fibronectins from human adult plasma, fetal plasma and from amniotic fluid obtained during early and late gestation were compared with respect to (i) their reactivity with lectins, (ii) their binding to the physiological ligands gelatin and heparin, and (iii) the role of the carbohydrate residues in the binding to these two ligands. The two fibronectin isoforms displayed distinct developmental differences in both glycosylation and binding properties: (i) Proportions of tri/tetraantennary complex glycans compared to the fraction of biantennary structures, as inferred from the reactivity with concanavalin A, were highest in amniotic fluid fibronectin from late pregnancy, lower in amniotic fluid fibronectin from early gestation, and even lower in fetal and adult plasma fibronectins. Likewise, fucose (alpha 1-6) linked to the innermost N-acetylglucosamine of the chitobiosyl core, defined by reactivity with Lens culinaris agglutinin (LCA), was present primarily in amniotic fluid fibronectin, and decreased in content during gestation from the 2nd. to the 3rd. trimenon. Both fetal and adult plasma fibronectins were only weakly reactive with LCA, indicating a low content of (alpha 1-6) linked fucose residues. After prior treatment with sialidase, both plasma and amniotic fluid fibronectins strongly reacted with erythrocyte phytohaemagglutinin (E-PHA), indicating that both fibronectin isoforms contain bisecting (beta 1-4) N-acetylglucosamine residues. Amniotic fluid fibronectins showed much greater reactivity than adult and fetal plasma fibronectins with wheat germ agglutinin; binding of this lectin to amnion fluid fibronectins was not decreased by desialylation indicating the presence of poly(N-acetyllactosamine) units. Whereas amniotic fluid fibronectins were strongly reactive with peanut agglutinin, neither adult nor fetal plasma fibronectins did bind to this lectin unless after prior desialylation. Hence, both fibronectin isoforms contain O-glycan residues that are fully sialylated in fetal and adult plasma fibronectins, but only partly sialylated in amniotic fluid fibronectins. According to these differences, glycosylation of plasma and amniotic fluid fibronectins is under developmental regulation. (ii) Amniotic fluid fibronectins had a significantly lower binding activity for both heparin and gelatin than plasma fibronectins. Moreover, amnion fibronectin from late gestation displayed a significantly lower binding to these two ligands than amnion fibronectin from early gestation. Fetal plasma fibronectins had a lower binding activity for gelatin than adult plasma fibronectin. (iii) Treatment of fibronectins with sialidase, fucosidase and removal of N-glycans with endoglycosidases H and F did not affect binding to gelatin and heparin, indicating that the interaction of plasma and amnion fibronectin with these two ligands is not influenced by their oligosaccharide moieties.

Adult↗

PubMed1989

Use of hepatocytes in adhesion and suspension cultures for liver support bioreactors.

Hepatocyte cultivation in bioreactors for hybrid liver support systems is possible under two conditions: attached to a substrate like membranes or microcarriers or in suspension culture. To compare the ammonia metabolism of hepatocytes cultivated under these two conditions, cultures of primary seeded rat hepatocytes were cultivated either attached to collagen coated tissue culture plastic or as a suspension culture. During the time course of culture, the ability of hepatocytes to reduce the ammonia content of the medium decreased in both adhesion and suspension cultures, though to different extents. In suspension cultures, ammonia content was reduced from 350 microM to about 100 microM (day 4) and to about 180 microM (day 6). No significant reduction was seen on day 8 of culture. In contrast, hepatocytes attached to collagen coated dishes remained viable and functional for at least 8 days after plating, reducing ammonia content from 350 microM to 70 microM (day 4), 90 microM (day 6) and 180 microM (day 8). The period of useful metabolism of hepatocytes in bioreactors for hybrid liver support systems appears to depend on the culture conditions.

Ammonia↗

PubMed1989

Selective isolation of individual cell surface proteins from tissue culture cells by a cleavable biotin label.

A method was developed to isolate cell surface proteins by a simple two-step procedure. Hepatocyte cell surface proteins were labeled by a cleavable biotin derivative in a covalent pulse reaction. Under the described conditions, NHS-SS-biotin proved to be an impermeant, cell surface-specific label which does not affect the impermeant, cell surface-specific label which does not affect the viability of rat hepatocytes. Biotinylated cell surface proteins could be selectively separated under non-denaturing conditions from non-biotinylated proteins and biotin-containing carboxylases by avidin affinity chromatography and sulfhydryl-mediated elution. Subsequent to alkylation of the eluted protein, individual cell surface proteins could be isolated by immunoprecipitation as shown for a selected Mr 120,000 glycoprotein gp120 of the hepatocyte plasma membrane. Using this technique, a transit time of gp120 from the endoplasmic reticulum to the cell surface of 2 h was determined. The results show that the combination of labeling with a cleavable biotin derivative, non-denaturing avidin affinity chromatography and immunoprecipitation is a useful method to isolate and study individual cell surface proteins.

Alkylation↗

PubMed1988

Demonstration of glycosylation variants of human fibrinogen, using the new technique of glycoprotein lectin immunosorbent assay (GLIA).

A new highly sensitive method, incorporation the ELISA technique (enzyme-linked immunosorbent assay), is described for the quantitation of the glycan residues of glycoproteins. With the aid of this "glycoprotein-lectin immunosorbent assay (GLIA)", it is possible to determine the nature of the glycan residues of a single protein in a glycoprotein mixture, without prior purification. The GLIA can be used for the accurate determination of the inhibitor constant for the interaction of any monosaccharide with any lectin. Using the described technique, glycosylation of human fibrinogen from plasma and amniotic fluid were compared. In fibrinogen from amniotic fluid a "fetal" glycosylation type could be demonstrated. In addition, evidence is presented for the first time that plasma fibrinogen possesses (GlcNAc beta 1----4Man beta) residues (bisecting GlcNAc) and O-glycosidically bound carbohydrate units. Preliminary results were published as abstract (E. Köttgen et al. (1988) Fresenius Z. Anal. Chem. 330, 448).

Enzyme-Linked Immunosorbent Assay↗

PubMed1988

Incorporation of non-acetylated hexosamines into plasma membrane glycoproteins of liver cells after galactosamine injection.

The following procedure for the detection of non-acetylated amino sugars in the plasma membrane was established: i) derivatization of free amino groups with dansyl-chloride, ii) hydrolysis with 3 M HCl (for 4 h at 105 degrees C) to liberate the dansylated carbohydrate moieties from the plasma membrane, iii) purification of the dansylated amino sugars by paper chromatography and subsequent analysis by thin-layer chromatography. Using this procedure, plasma membranes from rat liver were analysed after injection of D-[14C]galactosamine. For this purpose, rats were divided into three groups: the first received D-galactosamine.HCl at a dose of 2 mg/kg b.w., the second at a dose of 75 mg/kg b.w. and the third at a hepatitis-inducing dose of 260 mg/kg b.w.. In all three groups the majority of the protein-bound radioactivity in the plasma membrane was not dansylated, thus representing N-acetylated amino sugars. At a dose of 2 mg/kg, only 0.34% of the protein-bound radioactivity in the plasma membrane reacted with dansyl-chloride. At a dose of 70 mg/kg this value increased to 1.9%. At 260 mg/kg the value was 3.6%. These results indicate that the incorporation of non-acetylated amino sugar into the plasma membrane was dose-dependent and reached 90 pmol per mg plasma membrane protein during galactosamine injury. However, this incorporation of non-acetylated amino sugars into the plasma membrane did not represent a pathological mechanism responsible for the onset of the galactosamine-induced liver injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1988

[Results of interstitial radiotherapy using I-125 seeds in the treatment of prostatic cancer].

30 patients with localized adenocarcinoma of the prostate were treated with pelvic lymphadenectomy and I-125 interstitial implantation from 1980 to 1985 (21/30 T3-tumors and 14/30 with poor differentiation). The mean follow-up is 59.5 months (range 18 to 88 months). The crude, progression-free and local progression-free survival rates (Kaplan-Meier) for all patients are 68%, 61% and 71% respectively. But, the progression-free survival is 39% in patients with G3-tumors after five years and only 25% in patients with T3 G3-tumors after four years. The local progression rate was 33% in patients with T3-tumors. We did not observe any late intestinal side-effects, but 11/30 (37%) patients suffered from later urinary flow problems caused mainly by local tumor progression. Therefore, we regard interstitial implantation with I-125-seeds as an alternative treatment to radical prostatectomy in patients with T1, 2 G1, 2-tumors but as insufficient in patients with T3 G3-tumors.

Adenocarcinoma↗

PubMed1987

Role of membrane glycoproteins in mediating trophic responses.

During growth and differentiation the plasma membrane has a key role not only in the reception and transmission of extracellular signals such as hormones and growth factors, but also in communicating cellular response to the cellular microenvironment. Cellular response to trophic stimuli includes alterations of cell shape and cell surface antigenicity, of cell-cell recognition and cellular adhesion, of cell matrix binding and the adaptation of cell surface receptors. The plasma membrane is therefore regarded as a 'central agency' for the integration of a single cell into the complex system of a tissue or of an organism. The numerous functions of the plasma membrane are mainly mediated by membrane integrated glycoproteins or glycolipids both sharing the common feature of covalently bound oligosaccharide side chains. Specific alterations of oligosaccharide structure and metabolism associated with growth, differentiation and various pathologic conditions suggest a specific role for the oligosaccharide moieties in the regulation of cell surface functions (Table 1). This review intends to focus on the role of plasma membrane glycoproteins describing briefly principles of glycoprotein structure and function, and characteristics of their biosynthesis and degradation.

Animals↗

PubMed1987

Half-lives of L-[35S]methionine and L-[3H]fucose of transferrin in the serum of rats.

The half-lives of 35S-labelled L-methionine and of 3H-labelled L-fucose of serum transferrin of rats were measured in pulse-chase experiments in vivo. Both L-[35S]methionine and L-[6-3H]fucose disappeared from transferrin with nearly the same half-lives of 33.8 h and 36.5 h, respectively. The data show that in this major serum glycoprotein peripheral carbohydrates and the protein moiety are degraded as a unit.

Animals↗

PubMed1987

[Role of glycoproteins in the pathogenesis of peptic ulcer].

Glycoproteins are major constituents of the two-component mucous barrier: glycoproteins of the mucin-type rich in carbohydrate groups form the viscoelastic mucous gel of the mucosa, oligosaccharides of glycoproteins and glycosphingolipids embedded into the plasma membrane form the glycocalyx of the epithelial cell surface. Both structures are thought to play major roles in protecting gastric mucosa against luminal acid and proteases. This assumption is supported by experimental evidence for mucus glycoproteins, however is largely hypothetical for cell surface glycoproteins. Reports that biosynthesis of mucus glycoproteins is decreased during gastric ulceration, while breakdown is enhanced indicate that disorders of glycoprotein biosynthesis and degradation may contribute to the pathogenesis of peptic ulcer disease. The molecular mechanisms responsible for the observed alterations, however, are unknown. Possible alterations of glycoprotein metabolism that may occur at different stages of biosynthesis and degradation are discussed.

Animals↗