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

• Main Authors: Yoshiyuki Suzuki, Kunihiko Suzuki
• Format: Article
• Language: English
• Published: Elsevier 1972-09-01
• Series: Journal of Lipid Research
• Subjects: Gm2-ganglioside; asialo-Gm2-ganglioside; globoside
• Online Access: http://www.sciencedirect.com/science/article/pii/S0022227520393755

The galactose oxidase–sodium borohydride method was used to specifically label the terminal N-acetylgalactosamine of three glycosphingolipids, Gm2-ganglioside, asialo-Gm2-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-Gm2-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. Gm2-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 Gm2-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 Gm2-ganglioside suitable for metabolic studies. Thus, the method is useful for labeling not only terminal galactose but also terminal N-acetylgalactosamine of glycosphingolipids.