Labeling of soybean agglutinin by oxidation with sodium periodate followed by reduction with sodium [3-H]borohydride.

Periodate oxidation of soybean agglutinin, a glycoprotein lectin, resulted in destruction of up to 5 out of the 9 mannose residues present in each of its subunits (MW 30,000) without any loss of hemagglutinating activity. The oxidation did, however, abolish the interaction of soybean agglutinin with concanvalin A, as measured by quantitative precipitation. Reduction with sodium [3-H]borohydride of soybean agglutinin in which 4 out of 9 mannose residues per subunit were oxidized, afforded a radioactive product which retained full hemagglutinating activity and was indistinguishable from the native lectin by gel filtration, gel electrophoresis, and affinity chromatography. These results establish that the integrity of the carbohydrate side chain of soybean agglutinin is not essential for the biological activity of the lectin, and suggest a general method for the preparation of radioactive glycoprotein lectins.