FUNCTIONAL ACTIVATION OF ANTIBODIES ON MODIFICATION WITH PD(II) COPROPORPHYRIN-I N-HYDROXYSUCCINIMIDE ESTER

Metalloporphyrin-antibody conjugates provide a significant advantage o ver other types of conjugates in biomedical use for phosphorescence im munoassay, targeted immunotherapy, and internal imaging of malignant t umors. Monoclonal HSF102 antibody of mouse IgG2a subclass and monospec ific rabbit IgG, both antibodies directed to human spleen ferritin, we re modified with the new reagent Pd(II) coproporphyrin 1 tetra-N-hydro xysuccinimide ester. Functional study of the conjugates obtained revea led a 7- and 1.4-fold increase in the antigen binding activity for mon oclonal HSF102 and monospecific IgG antibodies, respectively. For rabb it monospecific IgG, a concomitant increase in binding to anti-rabbit Ige antibodies directed to the epitopes of the CH2 domain in the Fe fr agment was observed. In all cases, the maximum functional activation w as found after conjugating one mole porphyrin per mole antibody. These results suggest that functional activation of the conjugates might be due to an increase in conformational flexibility of an antibody molec ule after the modification. This increase in flexibility involves the Fab fragments and a pair of the CH2 domains in the Fc fragment and mig ht be due to a significant charge shift (minus 5 charge units per modi fied amino group) that occurs after conjugation of an antibody with te tracarboxylic porphyrin.