Protein-carbohydrate interaction. On the mode of bonding of aromatic moieties to concanavalin A, the phytohemagglutinin of the jack bean.

A number of meta-alkylphenyl ,8-D-glucopyranosides were synthesized and their ability to inhibit the concanavalin A-polysaccharide system was examined. The binding constants of these compounds as well as other substituted phenyl p-D-glucopyranosides were related to the hydrophobic (r) and electronic (u) nature of the substituents utilizing the equations devised by Hanschg and Hammettll respectively. Regression analysis of these relationships revealed that: (1) no linear correlation between the binding constants and the electronic properties of the aromatic substituents was evident; (2) the molecular volume of mono-ortho-substituents does not significantly effect the binding of aromatic p-D-glucopyranosides to concanavalin A; and (3) the hydrophobic nature (n) of orthoand metabut notparu-substituents is closely associated with the binding of aryl fl-D-glucosides to concanavalin A. It is proposed that apolar binding involving hydrophobic interactions associated with ovfho and meta but not with the para positions of the aromatic nucleus are the predominant forces involved in the binding of the phenyl moiety of phenyl fi-D-glucosides to concanavalin A. CONCANAVALIN A, the jack bean hemagglutinin, has been shown to interact with a select group of polysaccharides in a specific manner analogous to an antibody-antigen reaction.‘-g Recent reports from this laboratory 5*7,9*10 have indicated that the specificity of the protein involves the reversible polar binding (probably through hydrogen bonds) of the oxygen atoms of the C-l, C-2 and C-3 hydroxyl groups, the hydroxyl group at C-4 and the hydrogen atom of the C-6 hydroxyl of a-D-InZinnOpyranosyl residues. We have suggested that the aromatic aglycones of aand /3-D-glucoand mannopyranosides also bind to concanavalin A. In a study of the reaction of this protein with bovine serum albumin p-azophenyl glycoside-conjugates,’ it was noted that the azophenyl /3-D-glucopyranoside conjugate interacted with concanavalin A almost as avidly as the analogous a-anomer although earlier results5v9 indicated that methyl a-D-glucopyranoside binds to this protein to a much greater extent than the /3-anomer. These results suggested that the aromatic moiety probably interacts with the protein * This research was supported by a grant from the National Institutes of Health (AM-10171). t Present address: Department of Biochemistry, University of Kansas Medical Center, Kansas City, Kan. 66103, U.S.A. $ This work was done while this author was an Established Investigator of the American Heart Association, to whom inquiries regarding this paper should be sent. $j C. HANSCH and E. W. DEUTSCH, Biuchim. biophys. Acta 112, 381 (1966). I[ L. P. HAMMER, in Physical Organic Chemisfry, p. 184. McGraw-Hill, New York (1940).