Journal of Lipid Research, Vol. 13, 687-690, September 1972
Copyright © 1972 by Lipid Research, Inc.

Specific radioactive labeling of terminal N-acetylgalactosamine of glycosphingolipids by the galactose oxidase-sodium borohydride method

Yoshiyuki Suzuki and Kunihiko Suzuki

Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104

The galactose oxidase-sodium borohydride method was used to specifically label the terminal N-acetylgalactosamine of three glycosphingolipids, G_m2-ganglioside, asialo-G_m2-ganglioside, and globoside. All of the compounds showed a minimum of 95% radiopurity, and generally more than 90% of the total radioactivity was located in the terminal galactosamine moiety. Globoside and asialo-G_m2-ganglioside were labeled to high specific activities comparable with those of the sphingolipids with a terminal galactose moiety, labeled with the same procedure. These labeled compounds were well suited as substrates for the study of specific sphingolipid N-acetylgalactosaminidase. G_m2-ganglioside, however, was a poor substrate for galactose oxidase, and its specific activity was only a small percentage of the others. Furthermore, because of the low specific activity of the galactosamine moiety, it was necessary to pretreat G_m2-ganglioside with unlabeled sodium borohydride to reduce the nonspecific labeling of other portions of the molecule. The use of labeled sodium borohydride of a very high specific activity may yield specifically labeled G_m2-ganglioside suitable for metabolic studies. Thus, the method is useful for labeling not only terminal galactose but also terminal N-acetylgalactosamine of glycosphingolipids.

Supplementary key words G_m2-ganglioside • asialo-G_m2-ganglioside • globoside

Submitted on February 9, 1972
Accepted on April 28, 1972

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