INTERMICELLAR INTERACTION OF GANGLIOSIDE AGGREGATES AND STRUCTURAL STABILITY ON PH VARIATION

We have studied the effect of concentration and pH variations on micel lar structures of sialoglycosphingolipids (gangliosides) by using sync hrotron radiation small-angle X-ray scattering. We have treated four d ifferent aqueous dispersions of gangliosides containing monosialogangl iosides (G(M1)), disialogangliosides (G(D1a)) and two different types of the ganglioside mixtures. To discuss the change in the scattering c urve with concentration in the range of 0.1-10% w/v, we employed a res caled mean spherical approximation method (RMSA) for charged particle dispersions combined with a shell-modelling method. The present modell ing method well describes the characteristics of the whole experimenta l scattering curve, namely an intermicellar correlation peak at a very small angle and a rounded peak at a medium angle reflecting an intram icellar scattering density fluctuation. We determined simultaneously t he inter- and intra-micellar structures of the ganglioside aggregates under the repulsive screened Coulomb potential between them. The estim ated micellar surface charge is ca. 57 e in 0.01 M citrate buffer at p H 6.7, 25 degrees C. For every sample, the pH elevation from 3.6 to 8. 0 at 25 degrees C caused similar changes in the experimental scatterin g curve, gyration radius and distance distribution function, suggestin g a shrinkage of the micellar dimension and an intramicellar structura l change. The modelling analyses can explain the above changes mostly resulting from the change of the oligosaccharide chain portions in the micelles. The structural differences depending on the specimens, cont aining different ganglioside components are also clarified.