Physico-chemical and thermodynamic properties of monomeric concanavalin A.

An alkylated monomer of Concanavalin A was prepared photochemically according to the method of Tanaka et al. (1981). Its affinities for methyl-alpha-D-gluco, methyl-alpha-D-manno and p-nitrophenyl-alpha-D-manno pyranoside were calculated. The enthalpies of these binding reactions were measured calorimetrically and the thermodynamic parameters were calculated. The values obtained suggest that the structure of the monomer differs from that of the dimeric and tetrameric molecules. Calorimetric studies also showed that the monomeric derivative reacts with IgM but not IgG. The enthalpy per binding site in the monomer-IgM reaction is equal to that of the monomer-mannose derivative reaction; mannose is the terminal residue of the saccharide chains of the IgM molecule. The stoichiometry of the reaction is ten ConA-m per IgM molecule.