The interaction of concanavalin A with blood-group-substance glycoproteins from human secretions.

1. Gastric juice, saliva and ovarian-cyst fluid were fractionated into glycoprotein components by centrifuging to equilibrium in a caesium chloride density gradient. 2. The glycoprotein fractions from the gastric juice of two group O non-secretors, two group O secretors and three group A secretors all formed insoluble complexes with concanavalin A. 3. Fractions showing maximum interaction with concanavalin A had maximum blood-group activity measured by the haemagglutination-inhibition technique. The sulphate content of the gastric glycoproteins was unrelated to the capacity to interact with concanavalin A. 4. No interaction was found between concanavalin A and the glycoprotein fractions from any of the saliva or ovarian-cyst-fluid samples tested, implying that there is a structural difference in blood-group-substance glycoproteins in gastric juice when compared with those in saliva and ovarian-cyst fluid. 5. The protein components of each of the secretions tested, gastric juice, saliva and ovarian-cyst fluid, interacted with concanavalin A.