COVALENTLY CROSS-LINKED MONO-VALENT, DIVALENT, AND TETRAVALENT DERIVATIVES OF CONCANAVALIN-A

Dimeric [jack bean] succinyl-concanavalin [Con] A [jack bean] was cross-linked with ethylenediamine using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as a condensing agent. A divalent dimer and a tetravalent tetramer composed mostly of covalently cross-linked subunits bearing altered net charges were obtained. Photoaffinity labeling of the cross-linked dimer with p-azidophenyl .alpha.-D-mannopyranoside resulted in a specific label for its saccharide-binding site and yielded a nonvalent dimer and a monovalent dimer (showing no subunit exchange). Hemagglutination and glycogen precipitation data suggested that the labeled binding site was shielded but not destroyed by the label and could still bind weakly an external saccharide ligand, possibly due to unsteadiness of the shielding label. Although nonvalent and monovalent derivatives were mitogenic as were divalent and tetravalent derivatives for mouse splenic lymphocytes, binding and stimulation experiments indicated that their stimulating efficiencies after binding to the cells were far lower than of the multivalent counterparts. Their activities were inhibited by methyl .alpha.-D-mannopyranoside, suggesting that the weak activities of nonvalent and monovalent derivatives were due to the labeled sites entirely and partly, respectively. The triggering of lymphocyte mitogenesis by Con A may depend on cross-linkage of cell surface receptors.