D-Glucuronic acid: a non-inhibitor of the concanavalin A system.

The current use of concanavalin A, the phytohemagglutinin of the jack bean ~ , as a probe for investigating membranous glycoproteins and glycolipids requires a detailed knowledge of the protein's specificity. Extensive hapten inhibition studies employing monoand oligosaccharides and their simple derivatives demonstrated that the concanavalin A combining sites are complimentary to ct-D-mannopyranosyl and a-D-glucopyranosyl (or its 2-acetamido-2-deoxy derivative) residues with a specific requirement that the hydroxyl groups at the C-3, 4 and 6 positions of these sugars be unmodified 2-s . In a recent communication 6 it was reported that glucuronic acid is a better inhibitor than D-glucose of concanavalin A-polysaccharide interaction. I f this is true, it represents an important extension of the sugar-binding specificity of this protein. Since we had already shown 2, a that an unmodified C-6 hydroxymethyl group is an important concanavalin A binding locus we have reinvestigated the claim that glucuronic acid can serve as a substrate for concanavalin A. We report here our findings that low concentrations of glucuronic acid are noninhibitory, and that at higher concentrations the inhibitory action of glucuronic acid is nonspecific and can be explained by a depression of the pH of the incubation medium to a point where precipitation does not occur 7. The finding that D-glucuronic acid does not interact with concanavalin A gains added significance in the light of reports that certain charged, glucuronic acid-containing mucopolysaccharides form specific insoluble precipitates with concanavalin A 8, 9