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Biomedical subjects

H Wiegandt

Publications and source records attributed to H Wiegandt.

At least 91 records · Page 5Linked to original sources
PubMed1978

Studies on bovine brain membrane-bound neuraminidase (sialidase).

1) Lipophilic ganglioside GD1a (IV3NeuAc, II3NeuAc-GgOse4-Cer) is taken up by the cell membranes and hydrolyzed faster by membrane-bound neuraminidase than are water soluble substrates of the enzyme. 2) The enzymic breakdown of ganglioside GD1a is enhanced by general anesthetics whereas the degradation of the hydrophilic substrate sialyllactitol is reduced by these same agents. 3) General anesthetics lower the microviscosity of membranes as indicated by studies of fluorescence depolarisation with the indicator 1,6-diphenylhexatrien. Decreased microviscosity can result in a higher lateral diffusion of ganglioside GD1a, increasing its interaction with membrane-bound neuraminidase. 4) In vitro studies indicate that the activity of membrane-bound neuraminidase on gangliosides of brain membranes is regulated by the viscosity of these membranes and their monosialoganglioside content.

Animals↗
PubMed1978

Studies of ligand binding to cholera toxin, III. Cooperativity of oligosaccharide binding.

Binding parameters for the interaction of cholera toxin and choleragenoid with monosialo-gangliotetraose, the oligosaccharide moiety of ganglioside II3 NeuAc-GgOse4-Cer, have been measured by equilibrium displacement dialysis. The experimental data were evaluated by a curve fitting computer program. The binding curves obtained at 6 degrees C reflected positive cooperativity with average Hill coefficients in the range of 1.16 to 1.25. The cholera toxin as well as its ganglioside-binding protomer B-protein bind 4 mol of monosialogangliotetraitol per mol of protein. The presence of disulfide-cleaving agents like 2-mercaptoethanol did not eliminate the cooperativity of the binding characteristics, but increased the Hill coefficient.

Cholera Toxin↗
PubMed1978

Comparison of the interaction of mono- and oligovalent ligands with cholera toxin. Demonstration of aggregate formation at low ligand concentrations.

The stimulation by cholera toxin of adenylate cyclase in Chinese hamster ovarian cells could be inhibited by various ligands. The latter have been shown to contain the structural oligosaccharide entities required for binding to cholera toxin, established as Galbeta1 leads to 3GalNAcbeta1 leads to 4Gal3 comes from 2alphaNeuAc. The different inhibitory potency of the ligands thereby correlates with the size of the aggregates formed with the toxin, which in turn depends on the valency of the ligands. The conclusion is drawn from a comparison of the interaction of cholera toxin and its B-protomer with ganglioside II3NeuAc-GgOse4-Cer, the newly synthesized bis-(monosialo-gangliotetraityl)amine and monosialogangliotetraose. In a double diffusion test cholera toxin B-protomer precipitated with the ganglioside II3 NeuAcGgOSE4-Cer and the divalent ligand bis(monosialo-gangliotetraityl)amine, suggesting the formation of high molecular weight aggregates, whereas no precipitation was observed with the monovalent monosialo-gangliotetraose. By ultracentrifugation analysis, aggregate formation of the cholera toxin B-protomer could be demonstrated with the ganglioside II3 NeuAc-GgOse4-Cer and bis(monosialo-gangliotetraityl)amine at a concentration at which the ganglioside was assumed to be monodisperse. Ganglioside/cholera toxin B-protomer complexes sediment faster than those of the toxin and bis(monosialo-gangliotetraityl)amine, suggesting higher aggregation of cholera toxin B-protomer with the former. On the other hand, no sedimentation with monosialo-gangliotetraose was observed. By equilibrium displacement dialysis, however, a comparable high affinity of binding to cholera toxin B-protomer of both the mono- and divalent oligosaccharides was demonstrated. Furthermore, values for the maximal concentration of the bound ligand from these binding experiments with cholera toxin B-protomer established molar ratios of ligand to protein of 4 to 1 and 2 to 1 for monosialo-gangliotetraose and bis(monosialo-gangliotetraityl)amine, respectively. From the results it is concluded that the lipophilic moiety of the ganglioside is not directly involved in the binding process to the toxin protein but leads to an oligovalency of this ligand, due to formation of micellar or submicellar structures.

Adenylyl Cyclases↗
PubMed1977

Specific interaction of concanavalin A with glycolipid monolayers.

The effect of 131I-labelled concanavalin A on the surface pressure and surface radioactivity of monolayers formed from phospholipids and from natural and synthetic glycolipids has been studied. The lectin binds to and penetrates dipalmitoyl phosphatidylcholine monolayers at a surface pressure of 15 dynes/cm and this interaction is inhibited by the presence of alpha-methyl mannose in the subphase. At surface pressures of 25 dynes/cm or higher, concanavalin A will interact with monoglucosyl diglyceride or diglucosyl diglyceride from Acholeplasma laidlawii and with synthetic glycolipids containing 2 or 3 alpha 1 leads to 4-linked D-glucose residues in the headgroup, but not with phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, or with the ganglioside II3NeuAc-GgOse4-Cer. The binding to the glycolipid sugar group and penetration of the hydrocarbon region seem to occur simultaneously, as the time courses for the development of surface pressure and surface radioactivity coincide.

Cell Membrane↗
PubMed1977

Structure of tetanus toxin. II. Toxin binding to ganglioside.

The interaction between tetanus toxin and ganglioside containing 2 N-acetylneuraminic acid residues linked in sequence to one another has been investigated using a new method involving radioactively labeled ganglioside and tetanus toxin adsorbed to Sephadex matrix. Binding between the two components was demonstrated, and it was calculated that in the nanomolar concentration range, tetanus toxin becomes half-saturated at about 5 X 10(-8) M concentration of ganglioside. Removal of the ceramide portion from the ganglioside resulted in the complete loss of binding activity, whereas removal of the terminal N-acetylneuraminic acid residue from the intact ganglioside had no effect. Among the fragments derived from tetanus toxin (Helting, T. B., and Zwisler, O. (1977) J. Biol. Chem. 252, 187-193), only the heavy chain polypeptide exhibited a binding activity of the same order of magnitude as that observed for the native toxin. The light chain polypeptide showed no interaction with ganglioside and among the fragments derived from the toxin by digestion with papain, only Fragment C, at a high protein concentration, displayed marginal binding activity. Using monovalent antibodies directed against specific regions of the tetanus toxin molecule, it was demonstrated that antibodies directed against Fragment C uniquely interfere with the binding process. Anti-light chain serum was ineffective, as well as antitetanus toxoid serum previously absorbed with Fragment C. It is concluded that the binding site for ganglioside is located on the heavy chain portion of tetanus toxin, possibly in or near the region comprised by Fragment C.

Binding Sites↗
PubMed1977

Studies of the ligand binding to cholera toxin, II. The hydrophilic moiety of sialoglycolipids.

The binding between cholera toxin or its B-protein subunit and various ganglioside-related oligosaccharides was studied by equilibrium displacement dialysis. At low concentrations of ligand, the binding of monosialo-gangliotetraitol exceeded that of the parent ganglioside II3NeuAcGgOse4-Cer, the possible cell surface receptor for the toxin. The terminal galactose residue and an intact carboxyl group of the sialic acid moiety of monosialo-gangliotetraose were found to be necessary for strong binding to the toxin.

Chemical Phenomena↗
PubMed1976

Studies of the ligand binding to cholera toxin, I. The lipophilic moiety of sialoglycolipids.

The fixation of cholera toxin by ganglioside GGtet1 is dependent on the nature of the carbohydrate as well as the lipid moiety of the glycolipid. The role of the lipid in binding to the toxin investigated with synthetic ganglioside analogues (gangliosidoides). The interaction between glycolipid and toxin was followed by precipitate formation, by inhibition of toxicity and in polyacrylamide gel electrophoresis. For specific precipitation, an aliphatic hydrocarbon chain at least 14 C-atoms in length is required. Some of the gangliosidoides form high molecular weight complexes with cholera toxin at lower molar ratios of ligand to protein than the natural compound. None of the synthetic gangliosidoides equalled natural ganglioside in its ability to inhibit the effects of the toxin in vivo, but some did show considerable inhibitory activity ih monosialo-gangliotetraose or corresponding sialo-glycolipids prevents the easy degradation of the B-protein of cholera toxin into protein subunits by sodium dodecylsulfate.

Bacterial Toxins↗
PubMed1975

Studies of the subunit structure of choleragen.

The two choleragen protein constituents were isolated and characterized. Protein I has a molecular weight of approximately 54000. It consists of subunits of approximate molecular weight 10000. Protein II with molecular weight of approximately 32000 is cleaved by 2-mercaptoethanol into two fragments, protein II1 (N-terminal Asx, Mr = 25000) and protein II2 (N-terminal Ser, Mr = 7000). Proteins II1 and II2 could be recombined by oxidation to yield protein II. Upon treatment of choleragem with 2-mercaptoethanol protein II1 precipitates quantitatively. The remaining protein consisting of proteins I and II2, was quantitatively precipitated by ganglioside GGtet1. Of the separated choleragen subunit proteins, only protein I and not protein II complexed specifically with ganglioside GGtet1. The isolated proteins I and II were considerably less toxic in the skin test but almost full toxicity was recovered after mixing the two proteins I and II. Antisera against protein I and protein II revealed no immuno-cross reactivity between the two proteins. Both antisera inhibited the biological effects of choleragen in the skin and ileal loop tests. A molecular model for the constitution of choleragen is proposed.

Amino Acids↗