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M M Weiser

Publications and source records attributed to M M Weiser.

At least 91 records · Page 5Linked to original sources
PubMed1975

Role of cell membrane galactosyltransferase in concanavalin A agglutination of erythrocytes.

It has been previously observed that rabbit erythrocyte cell surface galactosyltransferase appears to play a role in concanavalin A agglutination of these erythrocytes (Podolsky et al., 1974). Further, a correlation between the occurrence or level of cell surface galactosyltransferase and concanavalin A agglutinability of other cell types has also been observed. The mechanism by which rabbit erythrocyte galactosyltransferase participates in concanavalin A agglutination has now been further defined. The enzyme was solubilized and purified. Characterization of the enzyme properties has shown them to be similar to those reported for other purified galactosyltransferases. Amino acid and carbohydrate analysis showed a high asparagine content and the presence of D-mannose. Specific alpha-mannosidase treatment of the enzyme showed that some of these D-mannose residues were terminal sugars. The purified enzyme also conferred concanavalin A agglutinability to non-agglutinable human erythrocytes. However, the ability to confer concanavalin A agglutinability was unrelated to the enzyme activity per se (as measured with fetuin acceptor) but appeared to be entirely dependent on the presence of terminal alpha-linked D-mannosyl residues in the enzyme structure. These findings suggest that the presence of terminal alpha-mannosidyl residues on cell surface glycoproteins such as galactosyltransferase may be the determining factor in agglutination of cells by concanavalin A.

Asparagine↗
PubMed1975

Adenylate and guanylate cyclase activities and cellular differentiation in rat small intestine.

Adenylate and guanylate cyclase activities were measured in rat small intestinal villus and crypt cells to determine possible correlations with cellular differentiation. Isolated intestinal cells were prepared by a method which effectively separates differentiated villus cells from undifferentiated crypt cells (J Biol Chem 248:2542, 1973). Crypt cells were found to have a significantly lower guanylate cyclase activity than villus cells. Adenylate cyclase activity was higher in crypt cells than villus cells, although the difference was less striking than the reverse gradient observed for guanylate cyclase. There was no gradient of activity for cyclic guanosine 3':5'-monophosphate phosphodiesterase. However, cyclic adenosine 3':5'-monophosphate phosphodiesterase activity was lower in villus cells. No villus to crypt gradient of cyclic adenosine 3':5'-monophosphate concentration was detected in mucosa frozen rapidly in liquid nitrogen. The properties and subcellular localization of the cyclases were also evaluated, and of particular interest was the localization of guanylate cyclase to the microvillus membrane and the confirmation of adenylate cyclase activity in the lateral-basal membrane. The villus to crypt gradient of guanylate cyclase suggests that this enzyme has a specialized role in the differentiated villus cell. The contrasting subcellular localization of the cyclases suggests that the cyclases may be interrelated, possibly reflecting the epithelial cell polarity for absorption and secretion.

Adenylyl Cyclases↗
PubMed1975

Intestinal villus and crypt cell responses to cholera toxin.

Adenylate cyclase activity was measured in rat small intestinal villus and crypt cells after in vivo and in vitro exposure to cholera toxin. The increase in intestinal adenylate cyclase induced by cholera toxin in vivo appeared to be largely confined to the villus cell with the largest increase observed for upper villus cells. Crypt cell adenylate cyclase was not responsive to cholera toxin. No response could be demonstrated for isolated villus or crypt cells incubated with cholera toxin in vitro. In vivo incubation with 125I-cholera toxin demonstrated binding to only villus cells. These results suggest that the major effect of cholera toxin was on villus cells rather than crypt cells and this was due to the greater accessibility or binding capacity of the villus cell to luminal cholera toxin.

Adenylyl Cyclases↗
PubMed1974

Galactosyltransferase and concanavalin A agglutination of cells.

A correlation has been observed between concanavalin A agglutination of various cell types and the presence of surface membrane galactosyltransferase (1-O-alpha-D-Galactosyl-myo-inositol:raffinose galactosyltransferase, EC 2.4.1.67) activity. Moreover, a reduction to less than 50% of cell surface galactosyltransferase activity occurred after treatment with concanavalin A; other cell surface glycosyltransferase enzyme activities examined were unaffected by concanavalin A treatment. To confirm the participation of cell surface galactosyltransferase in concanavalin A-induced cell agglutination, the enzyme from rabbit erythrocytes was solubilized by sonication and purified by preparative polyacrylamide gel electrophoresis. It was possible to achieve a purified preparation of rabbit erythrocyte galactosyltransferase by separation on concanavalin A-Sepharose. The purified enzyme showed visible immunoprecipitation (Ouchterlony) with concanavalin A. Furthermore, human erythrocytes, which are not normally agglutinated by concanavalin A, became agglutinable by the lectin when the erythrocytes were preincubated with purified galactosyltransferase. These experiments suggest a direct and possible specific role of cell surface galactosyltransferase enzyme in the mechanism of concanavalin A agglutination of cells.

Agglutination↗
PubMed1974

Cell surface galactosyltransferase and lectin agglutination of thymus and spleen lymphocytes.

Lectin agglutination and cell surface galactosyltransferase (EC 2.4.1.67; 1-O-alpha-D-galactosyl-myo-inositol:raffinose galactosyltransferase) enzyme activity have been studied with thymus and spleen lymphocytes of neonatal rats. Thymus lymphocytes were more agglutinable by concanavalin A than by wheat germ agglutinin, whereas spleen lymphocytes were more agglutinable by wheat germ agglutinin than by concanavalin A. Thymus lymphocytes, but not spleen lymphocytes, of neonatal rats could be blast transformed by concanavalin A. Cell surface galactosyltransferase activity was present on both types of lymphocytes, but was greatly increased on thymus cells after blast transformation. The differences in lectin agglutination suggest a difference in the surface membranes of thymus and spleen lymphocytes. The increase in cell surface galactosyltransferase activity with blast transformation of thymus lymphocytes may be related to the exteriorization of the Golgi apparatus into the plasma membrane.

Agglutination↗
PubMed1972

Concanavalin A agglutination of intestinal cells from the human fetus.

Concanavalin A markedly agglutinated isolated epithelial cells from the intestine of the human fetus but not from the intestine of the adult. Wheat germ agglutinin only moderately agglutinated cells from the intestine of an adult. These results extend the studies of concanavalin A agglutination of embryonic cells to human tissue, and they suggest that concanavalin A may be reacting with a common antigen on the fetal cell membrane.

Age Factors↗
PubMedDate not supplied

Crypt cell antigens (CCA): new carbohydrate markers for human colon cancer cells.

A panel of monoclonal antibodies produced against surface membrane components of the human colon tumor cell line Caco-2 was found to define oncofetal crypt cell antigens (CCA) expressed by fetal intestinal cells, adult small intestinal crypt cells, and human and rat colonic adenocarcinomas. The epitopes recognized by these antibodies have been identified as O-linked oligosaccharide chains associated with specific glycoproteins in cultured intestinal cells and in colon tumors in vivo. Analysis of a large group of normal and diseased human intestinal specimens has demonstrated a marked heterogeneity in CCA expression which correlated with the degree of organization of the tumor cells in the tissue, suggesting that the CCA represent useful histological and clinical markers for colon cancer.

Antibodies, Monoclonal↗
PubMedDate not supplied

Synthesis of intestinal basement membrane.

The rat small intestinal epithelial cell (enterocyte) has an average life span of 48h. Undifferentiated stem cells in the lower crypt region undergo division and differentiation into enterocytes as the cell moves on a basement membrane up the villus to reach the tip and be extruded into the lumen. The mechanism of this movement and relationship to basement membrane synthesis and/or renewal is unknown. This problem is discussed in regard to our findings suggesting that the major contribution to basement membrane synthesis and renewal may not be from the enterocyte.

Animals↗