11] Radioisotopic assay for galactocerebrosides and sulfatides

Abstract

This chapter presents the radioisotopic assay for galactocerebrosides and sulfatides. Combined galactose oxidase sodium borotritide labeling of galactosyl- and lactosylceramides approach exploits the ability of galactose oxidase specifically to introduce an aldehyde group as a result of oxidizing the C-6 position of the terminal galactose or galactosamine residue of sphingolipids. Radioactivity can be subsequently introduced by reducing the aldehyde group with sodium borotritide. This procedure can be employed principally for purposes of identification or qualitative analysis of galacto conjugates. Galactocerebrosides can be quantitatively oxidized by galactose oxidase, which can be quantitatively reduced with sodium borotritide to produce 3 H labeled galactocerebrosides. Sulfatides can also be quantitated by this procedure after methanolysis. The procedure allows the quantitation from 1-50 nmol of galactocerebrosides and sulfatides and can be conveniently and reliably used to determine 1 nmol of galactocerebrosides or sulfatides in a total lipid extract from brain tissue.