Cholera interaction

All earlier studies [155-158] reported the complexation of berberine with calf thymus DNA and suggested by a mechanism of intercalation. Maiti and coworkers [159-162] demonstrated first the base- and sequence-specificity of berberine from studies with several naturally occurring DNAs (Clostridium perfringenes, cholera bacteriophage 02, calf thymus, Escherichia coli, Micrococcus lysodeikticus) and synthetic DNAs ((poly(dG-dC) poly(dG-dC), poly(dG)-poly(dC), poly(dA-dT) poly(dA-dT), poly(dA)-poly(dT)) using various physicochemical techniques. Several aspects of the interaction were reported ... 

Figure 6.3. Mechanism of action of heterotrimeric G-proteins. Upon receptor occupancy, the Ga-subunit binds GTP in exchange for GDP, and then moves in the membrane until it encounters its target enzyme, shown here as adenylate cyclase (alternatively, a phospholipase). The activated target enzyme then becomes functional. Inherent GTPase activity within the a-subunit then hydrolyses bound GTP to GDP, and the a-subunit dissociates from its target enzyme (which becomes inactive) and rebinds the / - and ysubunits. Upon continued receptor occupancy, further catalytic cycles of GTP exchange and target enzyme activation may occur. The scheme shown is for a stimulatory G-protein (Got,), but similar sequences of events occur with inhibitory G-proteins (Gcx,) except that the interaction of the a-subunit with adenylate cyclase will result in its inhibition. The sites of action of pertussis and cholera toxins are shown.

Ellipsometry can follow the interactions between two types of biological macromolecules, the first of those two bound physically to the surface, the other acting from the solution. The binding of conconavalin A to adsorbed mannan 180) and of cholera toxin to adsorbed ganglioside t83) are examples. The adsorption of complement factors to an antibody-coated surface was monitored by ellipsometry and a modification of the same method was used for quantification of migration inhibition of human polymorphonuclear leucocytes 182). Interaction of proteins and cells with affinity ligands covalently coupled to silicon surfaces has been also studied 183). 

Cuatrecasas, P. Interaction of Vibrio cholerae enterotoxin with cell membranes. Biochemistry, 1973,12, 31 97-3558. 

Fishman, P.H. Moss, J. Osborne, J.C. Interaction of cholera-gen with the oligosaccharide of ganglioside GM1 Evidence for multiple oligosaccharide binding sites. Biochemistry, 1978,... 

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