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Biomedical subjects

R M Roberts

Publications and source records attributed to R M Roberts.

At least 271 records · Page 15Linked to original sources
PubMed1975

Complex saccharide metabolism in cystic fibrosis fibroblasts.

There are several reports of secretory and other abnormalities present in cultured fibroblasts from patients with cystic fibrosis (CF). We have, therefore, investigated aspects of complex saccharide synthesis and secretion by such cells compared with fibroblasts derived from heterozygous (HZ) parents and from normal (N) children. The main glycosaminoglycans produced by skin fibroblasts during in vitro culture were hyaluronic acid, heparan sulfates, and dermatan sulfate-like materials. Using double-label experiments with D-[3H]- or [14c]glucosamine and analyzing the products by ion exchange chromatography, it was shown for five CF, two HZ, and four N lines that these polysaccharides were secreted into the medium in approximately similar proportions to each other. Moreover, experiments in which three CF, nine HZ, and three N lines were grown in log phase for up to 5 days in the presence of [35S]sulfate and [3H]glucosamine indicate that, during such a period, CF fibroblasts do not secrete complex carbohydrates at rates significantly different from N or HZ cells. Neither do such cells shown an abnormal intracellular accumulation of complex carbohydrates. The latter observation was further confirmed by preparing whole cell autoradiographs during growth of six CF, two HZ, and three N lines in the presence of D-[3H]glucosamine and, subsequently, after addition of unlabeled medium.

Autoradiography↗
PubMed1973

Comparative studies on the carbohydrate-containing membrane components of normal and adenosine 3':5'-cyclic monophosphate-treated Chinese hamster ovary cells.

1. We investigated some of the changes in plasma-membrane composition that accompany the alteration in cell growth and morphology induced by treating Chinese-hamster ovary cells with dibutyryladenosine 3':5'-cyclic monophosphate (dibutyryl cyclic AMP). 2. A double-labelling technique was employed in which normal cells were given (14)C-labelled precursor, and those treated with dibutyryl cyclic AMP were given (3)H label. l-Leucine, d-glucosamine, and l-fucose were used to label the membranes. 3. After 3 days growth, the two populations of cells were harvested by trypsin treatment, the cells were pooled, and plasma membranes isolated. Proteins and glycoproteins of the membranes were separated by electrophoresis on sodium dodecyl sulphate-polyacrylamide gels, and the radioactive profiles for (14)C and (3)H and the staining patterns with Amido Black were compared. 4. Although certain components of the membrane from treated cells showed marked quantitative changes, there was neither major addition nor major deletions of components. 5. Complete proteolysis of the mixed membranes, of the material released from the cell surface by trypsin, and of the glycoproteins released from the cells into the medium, gave a series of radioactive glycopeptides when either fucose or glucosamine was employed as precursor. 6. After such glycopeptides were fractionated on columns of Sephadex G-50, marked differences in the elution profiles of (3)H and (14)C were noted. Dibutyryl cyclic AMP evidently causes alterations in the overall composition of the carbohydrate components of the cell surface. It was not possible to decide whether this was solely the result of the same glycoproteins being formed but in different proportions, or the result of modifications of oligosaccharide side chains on some of the glycoproteins. 7. Some of the changes were not unlike the reverse of those that accompany the transformation of fibroblasts by oncogenic viruses, and our results lend credence to the idea that the lowered amount of cyclic AMP noted in transformed cells is responsible for their altered surface properties.

Animals↗
PubMed1973

The Conversion of d-Glucose-6-C to Cell Wall Polysaccharide Material in Zea mays in Presence of High Endogenous Levels of Myoinositol.

When corn (Zea mays) roots are supplied with high concentrations of unlabeled myoinositol, the conversion of d-glucose-6-(14)C to cell wall galacturonic acid is significantly reduced compared to controls, although its incorporation into cell wall glucosyl units remains unchanged. This suggests that, in order to be converted to uronic acid, radiolabel from glucose must first pass through the internal myoinositol pool of the roots.

Journal Article↗
PubMed1972

Location of glycoproteins that contain glucosamine in plant tissues.

When radioactive d-glucosamine is provided to Acer pseudoplatanus cells in liquid culture in order to label those glycoproteins that contain amino sugars, it is incorporated predominantly into a crude cell wall fraction. This observation was confirmed histologically by preparing autoradiographs of thin tissue sections from plasmolyzed cells. Highly purified cell wall material from unlabeled cells has also been shown to contain small amounts of glucosamine. Similarly, about one-half of the amino sugar recovered from cultured cells of Nicotiana tabacum is present in their cell walls. In corn roots, however, the labeled glycoproteins that are formed after glucosamine incorporation are predominantly cytoplasmic and not deposited outside the protoplast.

Journal Article↗
PubMed1971

The formation of glycoproteins in tissues of higher plants. Specific labelling with D-(1- 14 C)glucosamine.

1. Radioactivity from d-[l-(14)C]glucosamine is incorporated into ethanol-insoluble compounds of high molecular weight in a number of plant tissues, including roots of corn (Zea mays), callus cells of sycamore (Acer pseudoplatanus), axenic cultures of duckweed (Lemna minor) and germinating seedlings of corn, broad bean (Vicia faba) and barley (Hordeum vulgare). 2. Except in the case of Lemna, where some of the radioactivity was recovered in glucose, hydrolysis of these ethanol-insoluble materials with acid released [(14)C]glucosamine as the major radioactive product. 3. The labelled compounds isolated from Zea roots and the Acer cells are believed to be glycoproteins rather than polysaccharides on the basis of their solubility properties, their charge characteristics and their susceptibility to hydrolysis by 0.5m-potassium hydroxide and by the proteases trypsin and Pronase. Further, radioactive peptides were isolated and purified after Pronase treatment and shown to contain glucosamine as well as a number of amino acids. 4. The experiments therefore indicate that d-[(14)C]glucosamine can be used as a specific precursor of the amino sugar units of plant as well as animal glycoproteins.

Alkalies↗
PubMed1971

Growth Inhibition and Metabolite Pool Levels in Plant Tissues Fed d-Glucosamine and d-Galactose.

The growth of corn (Zea mays) roots and barley (Hordeum vulgare) coleoptiles is sensitive to the presence of external d-glucosamine and d-galactose. In order to investigate this effect, tissues were fed the radioactive monosaccharides at concentrations that ranged from those that were strongly inhibitory to those that had little influence on growth. At low concentrations, d-glucosamine is converted to uridine diphosphate-N-acetyl-d-glucosamine, phosphate esters of N-acetylglucosamine, and free N-acetylglucosamine. As the external concentrations were increased, the pool levels of each of these metabolites rose several fold; and, in corn roots, two unidentified compounds, which had not been detected previously, began to accumulate in the tissues. The major products of d-galactose metabolism were uridine diphosphate-d-galactose and d-galactose 1-phosphate at all the concentrations tested. Both these compounds showed a marked increase as the external galactose concentrations were raised to inhibitory levels. The experiments indicate that efficient pathways exist in plants for the metabolism of d-glucosamine and d-galactose. These pathways, however, do not appear to be under strict control, so that metabolites accumulate in unusually high amounts and presumably interfere competitively with normal carbohydrate metabolism.

Journal Article↗