Action of galactose oxidase on galactolipids

Exposure of galactose-containing glycosphingolipids and certain glycoproteins to galactose oxidase followed by treatment with sodium borotritide has been used to label specifically the terminal galactose and N-acetylgalactosamine moieties of these glycoconjugates. This labelling procedure was shown to be ineffective with a lipid isolated from rat testis, 1-O-palmityl-2-O-palmitoyl-3 beta-galactosyl-glycerol, under conditions which resulted in excellent labelling of galactosyl-ceramide. Monogalactosyldiacylglycerol was also poorly labelled by this procedure. It was shown that neither 1-O-palmityl-2-O-palmitoyl-3 beta-(3'-sulfogalactosyl)-glycerol nor sulfogalactosyl-ceramide ("classical sulfatide") was labelled by this procedure indicating that sulfate substitution of the galactose inhibits the action of galactose oxidase. The labelling of galactosyl-ceramide was not inhibited in the presence of the galactoglycerolipid, sulfogalactoglycerolipid, or sulfatide. The property of the lipid aglycone responsible for inhibiting galactose oxidase action remains to be determined.