PHYSICOCHEMICAL PROPERTIES OF OX-BRAIN GANGLIOSIDES

Abstract

Gangliosides have been isolated from ox-brain grey matter in a high state of purity containing only traces of phosphatides and cerebrosides. They were separated into at least 5 components containing N-acetylneuraminic acid on thin-layer chromatography. The minimum molecular weight estimated from sedimentation in NN-dimethylformamide was 1500, which is close to the molecular weight calculated for gangliosides with 1 N-acetylneuraminic acid group/ceramide group. This also agrees well with the equivalent weight measured by titration. In water gangliosides formed spheroidal micelles that gave micellar weights of 250,000 to 450,000 calculated from sedimentation, diffusion and viscosity data. The chemical constitution of the individual ganglioside fractions appeared to influence the size of the micelles formed in water. A critical micelle concentration of about 0.015% was observed from measurement of the surface tensions of aqueous solutions. Subjecting gangliosides to mild acid hydrolysis removed half of the N-acetylneuraminic acid residues, resulting in a decrease in the charge on the micelles. The equivalent weight was increased to 3000. The removal of associated small ions resulted in changes in the physical properties of the micelles. Ultrasonic treatment of ganglioside solutions had no measurable effect on their properties. Gangliosides have been shown to interact with organic and inorganic cations and with other lipids. The significance of the physical properties of gangliosides in biological interactions and in their postulated role in cerebral tissues is discussed.