Protein-Carbohydrate Interaction

Abstract

Abstract Concanavalin A, a globulin found in the jack bean, reacts specifically to form a precipitate with a restricted group of branched polysaccharides. The various parameters optimal for this interaction were investigated by the quantitative precipitin method with a dextran as the precipitating polysaccharide. In this manner, an assay for concanavalin A activity was established. The analogy of this interaction with the antibody-antigen system is striking. A summary of findings follows. 1. Complete precipitation is achieved in 24 hours at 25°. 2. The pH range optimum for the reaction lies between 6.1 and 7.2. 3. The concentration of sodium chloride has no effect on the reaction when the system is buffered at pH 7.0 with phosphate. KI and KCNS, however, are inhibitory. 4. The presence of foreign proteins does not affect the total amount of concanavalin A precipitated. 5. The precipitate formed between concanavalin A and dextran is slightly soluble (1.5 µg of nitrogen per ml) at 25°. 6. More nitrogen is precipitated at 25° than at 0°, the relative amount depending upon the region of the equivalence curve examined.