Effect of Conditions of Extraction on the Extractability of Brain Gangliosides
It has been known for a long time that although gangliosides are freely soluble in water, they cannot be extracted from brain tissue, or from other tissues, by aqueous solutions, including 5% trichloracetic acid. Their extraction requires the use of organic solvents, mixtures of chloroform:methanol being the extracting mixture that has gained the widest usage (1). It has been accepted implicitly that these particular requirements for extraction of gangliosides indicate that they are bound to other tissue components, presumably proteins by ionic bonds through their strong carboxylic group, and by nonpolar bonds through the ceramide end of the molecule. The nonpolar bonds would make gangliosides unextractable by aqueous solvents. On the other hand, chloroform:methanol mixtures would dissociate the nonpolar bonds and the ionic bonds would be dissociated by the tissue electrolytes present in the extract. The closest demonstration of the occurrence of the ionic bonds has been provided by the work of Spence and Wolfe (2) who found that when tissue electrolytes have been removed by dialysis of the tissue homogenate, chloroform: methanol fails to extract gangliosides, except in small amounts, and that subsequent addition of KC1 and or NaCl restores the extractability of gangliosides by chloroform:methanol.
KeywordsSialic Acid Ionic Bond Lower Phase Biphasic System Pure Solvent
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