Interactions of G_M1 Ganglioside with Crude Rat Brain Neuronal Membranes

The binding of G_M1, ganglioside to crude preparations of rat brain neuronal membranes was studied, the following results being obtained: (a) the binding process followed a biphasic kinetics, which displayed a break at 0.07–0.08 X 10⁻⁶m G_M1, concentration; (b) the features of the binding process at G_M1, concentrations below the break and, over the break, above 10_‐6m appeared to be different. Below the break the process proceeded slowly and brought a stable and irreversible association of G_M1, molecules to the membranes. Over 10_‐6m the process was much more rapid and caused G_M1, molecules to interact in such a way that they were releasable by washing and could exchange with newly added free ganglioside; (c) the two binding processes displayed the characteristics of a saturation phenomenon; (d) in both cases, G_M1, taken up was freely available to galactose oxidase, indicating that the oligosaccharide chains protrude from the membrane surface. We postulate that G_M1, occurs, below and above the break, in different physical forms, each of them having a different mechanism of interaction with the membrane. Above 10_‐6m G_M1, interacts as micelles, and the basis of the micelle‐membrane inter action is a fusion process. Below the break, in the 10⁻⁸–10⁻⁷m range, the binding is the result of hydrophobic interactions between sites on the membrane and the hydrophobic portion of individual ganglioside molecules, most likely in the monomeric form. Toffano G. et al. Interactions of G_M1, ganglioside with crude rat brain neuronal membranes. J. Neurochem.35, 861–866 (1980).