Tryptophan fluorescence properties of cholera toxin upon interacting with ganglioside GD 1b

A blue shift of the tryptophan fluorescence emission spectra of cholera toxin or the B protomer is induced by disialoganglioside GD 1b with a capacity similar to that of monosialoganglioside GM 1 . Both gangliosides were also capable of decreasing or reversing the fluorescence quenching by iodide ion of the toxin. The quenching constants (K sv ) for the toxin fluorescence in absence of gangliosides was 2.8 M −1 ; in presence of GM 1 or GD 1b , K sv was 0.8 M −1 and 0.7 M −1 , respectively. Gangliosides GD 1a and GT 1b were unable to decrease the quenching effect. The results suggest that GD 1b induces a perturbation in the tryptophan environment of the toxin molecule similar to that induced by GM 1 .