The role of intermolecular electrostatic cooperative interactions causing cryoprecipitation of human monoclonal immunoglobin M

A chemical modification of carboxylic groups of monoclonal human cryoglobulin M has been studied. The modification by a chromophoric carbodiimide was accompanied by complete loss of IgM cryoprecipitating properties. The number of carboxylic groups important for biological activity was estimated by the Tsou method and found to be 2. The cryoprecipitation dependence on ionic strength has been investigated and the number of ions per binding site isolated upon formation of intermolecular ion couples has been estimated. Mechanism of cryoprecipitation stipulated by intermolecular cooperative electrostatic interactions is proposed.