The jack bean lectin Con A (ConA) and the Dioclea grandiflora lectin (DGL) are highly homologous Man/Glc-specific members of the Diocleinae subtribe. Both lectins bind, cross-link, and ppt. with carbohydrates possessing multiple terminal nonreducing Man residues. The present study investigates the binding and crosslinking interactions of ConA and DGL with a series of synthetic divalent carbohydrates that possess spacer groups with increasing flexibility and length between terminal a-mannopyranoside residues. Isothermal titrn. microcalorimetry was used to det. the thermodn. of binding of the two lectins to the divalent analogs, and kinetic light scattering and electron microscopy studies were used to characterize the crosslinking interactions of the lectins with the carbohydrates. The results demonstrated that divalent analogs with flexible spacer groups between the two terminal Man residues possess higher affinities for the two lectins as compared with those with inflexible spacer groups. Furthermore, despite their high degree of homol., ConA and DGL exhibit differences in their kinetics of crosslinking and pptn. with the divalent analogs. Electron microscopy shows the loss of organized cross-linked lattices of the two lectins with analogs possessing increased distance between the terminal Man residues. The loss of lattice patterns with the analogs is distinct for each lectin. These results have important implications for the interactions of lectins with multivalent carbohydrate receptors in biol. systems. [on SciFinder (R)]