Behavior of sugar derivatives in procedures for ganglioside isolation

A common method of studying ganglioside metabolism is to measure the amounts of radioactivity incorporated into ganglioside from a radiolabeled precursor. This requires that radioactive nonganglioside material be completely removed from the ganglioside fraction. Nucleotide sugars and aminosugars comprise an important source of such contaminants. Therefore, we have studied their behaviors in several procedures currently employed to isolate gangliosides. Over 50% of the radioactivity associated with several nucleotide sugars added to a brain homogenate is extracted with chloroform/methanol (2:1, v/v), and most of this is recovered in the upper phase of a Folch partition. Dialysis against water removes almost all of the free aminosugar but only 70% of nucleotide sugar. Treatment with alkaline phosphatase, phosphodiesterase and alkaline methanol followed by dialysis removes almost all of the nucleotide diphosphate sugars but only 88% of cytidine 5'-monophosphate sialic acid (CMP-NeuAc). Nucleotide sugars cannot be separated from gangliosides by Unisil or Iatrobead chromatography, but nucleotide diphosphate sugars and gangliosides are resolved with Sephadex LH-20 chromatography following treatment with phosphodiesterase and alkaline phosphatase. CMP-NeuAc was not satisfactorily separated from gangliosides using any of the procedures.