[Chemical modification of antibodies against carcino-embryonal antigen]

Chemical modification of different amino acid residues and the carbohydrate moiety of antibodies to carcino-embryonic antigen (CEA) was used to elucidate their role in the interaction with CEA and to evaluate the effect of antibody modification and steric factor in immunosorbent synthesis. The distribution of the modified groups among the structural fragments of IgG and the levels of changes in the antigen-binding properties of modified antibodies were investigated. The Fc-fragment of IgG was shown to contain carboxylic groups, tyrosine and histidine residues, whose modification influences the antigen-binding properties as a result of generalized conformational changes in the IgG molecule. A comparison of these results with earlier obtained data on the functional properties, of immobilized antibodies revealed that the decrease of antigen-binding characteristics of anti-CEA after IgG immobilization via NH2- and COOH-groups, carbohydrate moiety, tyrosine and histidine residues is due to the direct effect of antibody modification, whereas the changes in parameters of antibody interaction with antigen after IgG immobilization via SH-groups, methionine and histidine residues is due to steric hindrances.