In vitro radiolabeling of galactosyl and N-acetylgalactosaminyl moieties of glycoproteins with carbon-14.

The primary alcohol group on the carbon 6 of terminal galactosyl and N-acetylgalactosaminyl moieties of glycoproteins can be oxidized to an aldehyde by treatment with galactose oxidase. By reacting these aldehyde groups with 14C-labeled sodium cyanide, 14C-labeled cyanohydrin derivatives were obtained. Similarly, reduction of these aldehyde groups with tritiated sodium borohydride following standard procedures, yields 3H-labeled glycoproteins. 14C- and 3H-labeled derivatives of asialofetuin and asialo ovine submaxillary mucin with high specific radioactivities were prepared using these procedures. Mixtures containing microgram amounts of 14C- and 3H-labeled glycoproteins were subjected to column chromatography and gradient ultracentrifugation and the position of the individual glycoproteins was determined by simultaneous counting for 14C and 3H. These experiments demonstrate the usefulness of this approach for comparative analytical studies using biological specimens available in minute quantities.