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Biomedical subjects

H Baumann

Publications and source records attributed to H Baumann.

At least 253 records · Page 14Linked to original sources
PubMed1980

Insertion of biologically active membrane proteins from rat liver into the plasma membrane of mouse fibroblasts.

Phospholipids, glucolipids, and total proteins were separated from a plasma membrane fraction of rat liver. Membrane glycoproteins were isolated from deoxycholate extracts of rat liver membranes and hepatoma tissue culture membranes by concanavalin A chromatography. The membrane glycoprotein on hepatocytes that acts as a receptor for serum glycoproteins have lost their terminal sialic acid was also purified from rat liver membranes. Closed membrane vesicles were reconstituted from mixtures of deoxycholate-solubilized phospholipids and proteins by dialysis and purified by isopycnic centrifugation. The orientation of the proteins and glycoproteins in these reconstituted vesicles was examined by their accessibility to trypsin and neuraminidase and by their ability to be released from the vesicle by different concentrations of detergent. Most of the proteins are embedded in a right-side-out orientation in the lipid bilayer. The reconstituted membrane vesicles can be fused to mouse L-cells with polyethylene glycol. The extent of fusion is a function of the phospholipid:protein ratio in the reconstituted vesicles. After fusion, the phospholipid component of the vesicles mixes relatively rapidly with cell membrane lipids as judged by the immunofluorescence pattern of cells fused with lipid vesicles containing trinitrophenylated lipids. In contrast, proteins transferred to L-cells show restricted diffusion as judged again by immunofluorescence techniques. The metabolic turnover of proteins and glycoproteins after transfer to the plasma membranes of mouse L-cells was examined by radioisotopic methods. Total rat liver membrane proteins are very stable after transfer to the L-cells. Some of these proteins may be involved in the formation of an exoskeleton at the cell surface. Hepatoma tissue culture cell glycoproteins after transfer to the L-cells are less stable in terms of turnover properties than are total liver membrane proteins. However, some of these proteins are released into the medium as large molecular weight material rather than being degraded to small molecular weight, acid-soluble component. The receptor for serum asialoglycoproteins is relatively stable after transfer in reconstituted vesicles to the membrane of L-cells. Most of this hepatocyte-specific membrane glycoprotein is degraded to acid-soluble material with a half-life in the L-cell of at least 50 h. Transfer of the purified receptor in reconstituted vesicles to L-cells confers upon the recipient cell the biological activities specified and initiated by these receptors in hepatocytes.

Animals↗
PubMed1980

Metabolic fate of cell surface glycoproteins during immunoglobulin-induced internalization.

Goat antibodies directed against a subset of the externally oriented plasma membrane glycoproteins of hepatoma tissue culture (HTC) cells were used to follow the metabolic fate of the membrane antigens and the specifically bound immunoglobulin molecules in this cell type in cultures. Analyses of the immunoprecipitates from cells labeled in situ with neuraminidase and galactose oxidase, followed by reduction with tritiated sodium borohydride, indicate that about 40% of the galactose-labeled plasma membrane glycoproteins are recognized by the antiserum. Fluorescent microscopic analyses of cells treated with fluorescein-conjugated immunoglobulins and analyses of trypsin accessibility indicate that probably all of the antibodies bound to the cell surface are patched and internalized within about 4 hr when the cells are subsequently cultured at 37 degrees C in the presence of rabbit anti-goat immunoglobulins. At the same time, the antigens are also interiorized. Analyses of the cellular localization of the interiorized antigens and antibodies by cell fractionation on Percoll gradients show that the immunoglobulins to the cell surface antigens and the antigens themselves migrate to the same region of the Percoll gradient as lysosomal hydrolases. Although the antibodies bind to the cell surface glycoproteins and bring about patching and interiorization, there is no effect on the degradation of the plasma membrane antigens labeled via the galactose oxidase/borohydride reduction method. Furthermore, the iodinated antibodies directed against these membrane glycoproteins behave in their turnover properties like membrane antigens; the cell-bound specific immunoglobulins have the same half-life as the membrane glycoproteins. When the cells that had been reacted with the goat antibodies to membrane glycoprotein were cultured in the presence of rabbit anti-goat immunoglobulins, degradation of the former antibodies was effectively decreased. Similar results were obtained with concanavalin A and antibodies directed against this plant lectin.

Animals↗
PubMed1980

Dexamethasone regulates the program of secretory glycoprotein synthesis in hepatoma tissue culture cells.

The secretory glycoproteins synthesized by hepatoma tissue culture (HTC) cells were resolved by two-dimensional polyacrylamide gel electrophoresis of media from cells that were grown in the presence of [(3)H]fucose. These cells synthesize and secrete a complex set of fucose-containing glycoproteins. These secretory glycoproteins are distinct from those glycoproteins present in the plasma membrane of HTC cells. Incubation of HTC cells with dexamethasone has a pronounced effect on the quality and quantity (denoted here as the program) of secretory protein synthesis, as assayed by the short-term incorporation of labeled mannose, fucose, or methionine. The synthesis of two mannose- and fucose- containing glycoprotein series, one of 50,000 mol wt and a more heterogeneous series with mol wt of 35,000-50,000, is increased to a high level by the hormone; conversely, the synthesis of other secretory proteins, particularly one with mol wt of 70,000, is decreased or stopped completely. The synthesis of some major secretory proteins is not affected by the hormone. Dexamethasone has less of an effect on the composition of either total cell membrane glycoprotein or plasma membrane glycoprotein. But there is a decrease in the synthesis of a major membrane glycoprotein series with mol wt of 140,000. These effects of dexamethasone are relatively specific to HTC cells. Neither Reuber H-35 cells nor primary cultures of rat hepatocytes show the same response to the steroid. Two variant HTC cell lines, which were selected for their resistance to dexamethasone inhibition of extracellular plasminogen activator activity, respond only partially to the steroid-induced regulation of the secretory and membrane glycoproteins.

Animals↗
PubMed1979

Effect of trypsin on the cell surface proteins of hepatoma tissue culture cells. Characterization of a carbohydrate-rich glycopeptide released from a calcium binding membrane glycoprotein.

Concentrations of trypsin that bring about aggregation of hepatoma tissue culture (HTC) cells also release from the cell surface an Mr = 55,000 glycopeptide fragment. This glycopeptide fragment also accumulates in the medium, including serum-free medium, as a normal consequence of membrane protein turnover. The trypsin-released glycopeptide is labeled when cells are grown in the presence of fucose or leucine before treatment of the cells with the protease. Similarly, the glycopeptide fragment can be labeled by reacting cells in situ by lactoperoxidase-catalyzed radioiodination or by tritiated borohydride reduction of cells treated first with neuraminidase and galactose oxidase. The tryptic glycopeptide fragment was purified by concanavalin A-Sepharose chromatography, and hydroxyapatite chromatography in the presence of dodecyl sulfate. The amino acid and carbohydrate composition was determined, as was the sensitivity of the purified glycopeptide to a variety of endo- and exoglycosidases. The purified glycopeptide contains an average of 17 sialic acid residues and hence, shows charge heterogeneity after electrophoresis in isoelectric focusing gels. The charge heterogeneity can be eliminated completely by treatment with neuraminidase. The glycopeptide after this treatment is homogeneous. The trypsin-sensitive membrane glycoprotein which is the source of the Mr = 55,000 glycopeptide was identified by two-dimensional gel electrophoretic analysis of labeled cells, treated or not treated with trypsin. This glycoprotein, which has an apparent molecular weight of 85,000 and forms a homodimer in the presence of calcium ions, was purified and its identity as the parent of the Mr = 55,000 glycopeptide was confirmed by showing that the same Mr = 55,000 fragment was released by trypsin from the purified glycoprotein as was released from the intact cells.

Amino Acids↗
PubMed1979

Biosynthesis of membrane glycoproteins in rat hepatoma tissue culture cells.

The early steps in the biosynthesis of glycoproteins associated with the plasma membranes of rat hepatoma tissue culture cells has been analyzed. By measuring the effect of tunicamycin on the incorporation of [3H] mannose and [3H] fucose into cell glycoproteins, it was determined that an interval of about 1 h was required to transfer the glycoprotein from site of mannosylation to the site of fucosylation. This result was corroborated by an analysis of the time required for the appearance of either mannose or fucose-labeled glycoproteins at the cell surface. The separation of membrane glycoproteins by a two-dimensional gel system allowed the visualization of the modifications leading to both size and charge heterogeneity of these proteins. By following the changes in electrophoretic mobility introduced into membrane glycoproteins during a chase period after a pulse labeling, the time course of these molecular alterations could be estimated. Several glycoproteins have apparently higher rates of synthesis than the bulk of membrane-associated glycoproteins. Most of these glycoproteins were released within 2 h after biosynthesis from the intracellular membrane fraction and appear after 3 h in the medium. In addition to the glycoproteins that contain both mannose and fucose and that show a high degree of charge heterogeneity, there are other membrane-bound species that are not noticeably modified by the incorporation of fucose or sialic acids. These glycoproteins could represent constituents limited to the internal membrane system of the HTC cell.

Animals↗
PubMed1979

Neutral fucolipids and fucogangliosides of rat hepatoma HTC and H35 cells, rat liver, and hepatocytes.

Neutral fucolipids and fucogangliosides of normal rat liver, normal rat hepatocytes, and rat hepatoma H35 and HTC cells have been compared. H35 cells were characterized by accumulation of a relatively large quantity of a few neutral fucolipids and a major fucoganglioside. HTC cells were characterized by accumulation of several neutral fucolipids and by the absence of fucogangliosides. Those fucolipids which accumulated in hepatoma cells were absent in normal rat liver and normal hepatocytes. Normal hepatocytes and normal rat liver contained a low quantity of fucolipids which migrated differently on thin-layer chromatography from those which accumulated in hepatoma cells. In addition to these qualitative differences, the quantity of total fucose in purified glycolipid fraction was much higher in H35 and significantly higher in HTC cells than that in rat liver. A fucoganglioside which accumulated in H35 cells was tentatively characterized as a fucosylated GM1 ganglioside with the following structure: (formula: see text). The results indicate that anomalous fucosylation on glycolipid may take place in hepatoma cells.

Animals↗
PubMed1978

Surgical problems in necrotizing enterocolitis in childhood.

The problem of necrotizing enterocolitis is discussed based on the experience with 24 patients. It has been found that the time factor plays an important role in the decision whether to operate. The indications for operation are intestinal perforation, threatening perforation, and penetration of a covered perforation. Operation is carried out in order to treat the peritonitis caused by perforation. The various operative methods are described and evaluated. Intestinal resection, exclusion enterostomies, and suture of the perforation may all be justified, depending on the findings at operation. The difficulties in the differential diagnosis are discussed. The importance of late complications are stressed, and it is pointed out that every case will require routine controls long after discharge from the hospital. The high mortality is directly related not to the surgical complications, but rather to the septicemia which so often develops.

Diagnosis, Differential↗