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Biomedical subjects

W Reutter

Publications and source records attributed to W Reutter.

At least 181 records · Page 10Linked to original sources
PubMed1981

Inhibition of in vitro biosynthesis of N-acetylneuraminic acid by N-acyl- and N-alkyl-2-amino-2-deoxyhexoses.

The biosynthesis of N-acetylneuraminic acid is markedly inhibited by 2-deoxy-2-propionamido-D-glucose (GlcNProp) and to a much lesser extent by 2-deoxy-2-propionamido-D-mannose (ManNProp), but not by 2-deoxy-2-propionamido-D-galactose and N-methylated derivatives of 2-amino-2-deoxy-D-glucose. 2-Deoxy-2-trimethylamino-D-glucose is a weak inhibitor of 2-acetamido-2-deoxy-D-mannose metabolism. When incubated in a cell-free system from rat liver, GlcNProp gives the 6-phosphate, which is converted into N-propionylneuraminic acid. Evidence is presented which shows that it is the metabolites GlcNProp-6-P and ManNProp-6-P which are the competitive inhibitors, and not GlcNProp itself.

Animals↗
PubMed1980

Different turnover of fucose residues in plasma membranes of rat liver and Morris hepatoma 7777.

Half-lives and rate constants of degradation of protein-bound fucose have been determined in plasma membranes and total cell homogenates of rat liver and Morris hepatoma 7777. The existence of at least two dynamically different classes of fucose-containing glycoproteins could be demonstrated in both liver and hepatoma plasma membranes. The apparent half-lives were 8.4 and 24.5 h (host liver) and 11.5 and 33.9 h (Morris hepatoma). Since this biphasic loss of fucose residues was not observed for sialic acid [Harms & Reutter (1974) Cancer Res. 34, 3165--3172], the differences are possibly related to specific functions of fucosylated glycoproteins of the plasma membrane.

Animals↗
PubMed1980

Different half-lives of the carbohydrate and protein moieties of a 110,000-dalton glycoprotein isolated from plasma membranes of rat liver.

By using a four-step procedure (i, solubilization with Triton X-100; ii, affinity chromatography on concanavalin A-Sepharose; iii, affinity chromatography on wheat germ lectin-Sepharose; iv, preparative sodium dodecyl sulfate gel electrophoresis) a glycoprotein was isolated from rat liver plasma membrane. The molecular weight is 110,000 and the isoelectric point is 5.8. It contains L-fucose, N-acetylneuraminic acid, D-galactose, D-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and considerable quantities of aspartate, threonine, serine, and leucine. In pulse-chase experiments the half-lives of methionine and arginine, representing the half-life of the protein, were determined as 70 hr and 78 hr, respectively. The half-lives of the terminal carbohydrates L-fucose and N-acetylneuraminic acid were 12.5 and 33 hr, respectively. The galactose half-life was 20 hr. From this it is concluded that terminal sugars turn over several times in the life-span of this protein molecule. This process may be operative during membrane recycling mechanisms.

Animals↗
PubMed1980

A colchicine-sensitive uptake system in Morris hepatomas.

The interference of microtubular disruptors with the uptake of amino acids and other low molecular weight substrates has been studied in Morris hepatomas, host liver, and regenerating liver. Colchicine inhibits amino acid transport (alpha-aminoisobutyric acid, L-methionine, and L-leucine) in hepatomas by 59-98% whereas transport in host and regenerating liver is not impeded but increased. In hepatomas, treatment urea, and carbonate. Vinblastine, but not lumicolchicine or cytochalasin B, is an effective inhibitor. The inhibition of uptake is not linked to a decrease of cellular ATP and UTP. The data suggest that the transport of low molecular weight substrates in hepatomas is related to microtubules or other colchicine-binding structures, e.g., of the plasma membrane. This colchicine-sensitive uptake system in hepatomas may be due to the malignant transformation of hepatocytes.

Amino Acids↗
PubMed1980

Conversion of 14C-galactose into amino acids in tissue culture cells and its inhibition by manganese.

The incorporation of 14C-galactose into primary AGMK-cells was studied in the presence and absence of Mn2+. The transport of galactose into the cells is not influenced by Mn2+. 1 mM MnCl2 inhibits the incorporation of galactose into acid-precipitable material up to 50% after 6 hours incubation. In the absence of Mn2+ a substantial amount of galactose is converted to glucose, which is mainly metabolized into aspartic acid and serine. The conversion of galactose into glucose is inhibited by the addition of Mn2+. However, Mn2+ does not influence the activity of the UDP-galactose-4'-epimerase in vitro. Using the SDS-polyacrylamide electrophoresis the labelling of protein bands is similar with 14C-galactose or a 14C-amino acid mixture, respectively. In the presence of Mn2+ the incorporation of both galactose or amino acids is inhibited: With amino acids the inhibition is observed in all protein bands, whereas with galactose some bands remain unaffected. It is concluded that these are galactoproteins.

Amino Acids↗
PubMed1979

[Glycoproteins: their biological and clinical significance. I (author's transl)].

Increasing knowledge on structure, biosynthesis and catabolism of glycoproteins have given new insights on the patho-biochemical and clinical significance of these macromolecules. The most important results and conclusions are summarized in this review. 1. The terminal sugars of glycoproteins--N-acetylneuraminic acid (NANA) and L-fucose--as well as the penultimate galactose molecule have important functions in cell interaction, adhesion and recognition. Moreover, these carbohydrates mediate the migration and distribution of cells and it is believed that they are essential part of the feto-maternal "immunological barrier". 2. Evidence indicating that the composition and pattern of plasma membrane glycoproteins is associated with tumour growth and metastatic formation is accumulating. Moreover, the determination of serum glycosyltransferase activity is gaining increasing interest, because the level of these enzymes is substantially elevated in patients with neoplastic disease. 3. Diseases of the autoimmunosystem are likely linked to a disturbed glycoprotein metabolism. The clinical importance is underlined by studies on immunotherapy of tumours.

Autoimmune Diseases↗
PubMed1979

Galactosamine-induced sensitization to the lethal effects of endotoxin.

Treatment of rabbits, rats, and mice with D-galactosamine increased their sensitivity to the lethal effects of lipopolysaccharide several thousand fold. The susceptibility of the animals was highest when the lipopolysaccharide was injected together with galactosamine and decreased successively when injection was carried out 1, 2, and 3 hr later. Sensitization was absent when the lipopolysaccharide was administered 1 hr before or 4 hr after galactosamine. The onset of lethality after treatment with galactosamine and lipopolysaccharide occurred faster than with lipopolysaccharide alone; usually all animals died 5-9 hr later. The galactosamine-induced sensitization to lipopolysaccharide could be reversed by uridine which is known to inhibit the early biochemical alterations induced by the amino sugar in the hepatocytes. Although galactosamine is known to exhibit hepatotoxic activity inducing ultimate necrosis of the hepatocytes, the data so far suggests that the sensitization to lipopolysaccharide is related only to the early metabolic effects of the hexosamine.

Animals↗
PubMed1978

On the pathogenesis of galactosamine hepatitis. Indications of extrahepatocellular mechanisms responsible for liver cell death.

In order to evaluate the pathogenesis of galactosamine hepatitis, the action of galactosamine on mast cells, and alteration in the complement system suring the course of this experimental injury were studied. It has been previously demonstrated that rat livers after colectomy are refractory to galactosamine-induced liver cell necrosis and inflammation. For this reason colectomized animals were used to see whether the biochemical alterations produced by this aminosugar and thought to be responsible for cell death developed. Results showed: 1. galactosamine potently degranulates mast cells in vivo and in vitro, 2. the complement system is a) activated during the course of galactosamine hepatitis, probably by circulating endotoxins, and b) is essential for liver cell death in galactosamine hepatitis, and 3. colectomy does not prevent biochemical changes known to occur during galactosamine metabolism. It is concluded that death of galactosamine-injured liver cells is triggered by extrahepatocellular mechanisms, which lead ultimately to an activated complement system by endotoxins. It is postulated that related mechanism may also occur in viral hepatitis and in fulminant hepatic failure in man.

Animals↗