Laser-light scattering investigation of the micellar properties of gangliosides

The micellar properties of gangliosides in water solutions were investigated by quasielastic light scattering measurements. G_M1 and G_D1a gangliosides were isolated from calf brain, purified to more than 99% and dissolved in 0.025 M Tris-HCI buffer (pH 6.8) at 37°C. The average intensity of scattered light and the intensity correlation function were measured by an apparatus including a 5145 Å argon laser and a real-time digital correlator. The scattered intensity data allowed the derivation of an upper limit to the critical micelle concentration (c₀) and the evaluation of the molecular weight (M) of the micelle. The intensity correlation function gave the diffusion coefficient D, and hence the hydrodynamic radius R_H, and also contained information on the polydispersity of the sample. We find c_o <1 × 10^-6 M for both G_M1 and G_D1a, M = 532 000 ± 50 000 and R_H = 63.9 ± 2 A ̊ for G_M1, and M = 417 000 ± 40 000 and R_H = 59.5 ± 2 A ̊ for G_D1a. The mixture 3:1 of the two gangliosides gave intermediate values for all examined parameters. The presence of cations, within the physiological concentration range. and, in particular of Ca²⁺, did not influence significantly the values of c_o and the main features of the micelle.