MICROHETEROGENEITY OF MOUSE ANTIDEXTRAN MONOCLONAL-ANTIBODIES

Mouse antidextran monoclonal antibodies showed microheterogeneity whic h was analyzed by two-dimensional polyacrylamide gel electrophoresis ( 2-D PAGE). Not only the heavy (H) chains but also the light (L) chains were heterogeneous in terms of isoelectric point (pi). The higher the pr, the more prominent the H chain spots. To demonstrate the cause of the microheterogeneity an IgG1 monoclonal antibody (mAb 35.8.2H) was examined especially for involvement of the sugar moiety in the microhe terogeneity. The glycosylated region was determined in the Fc portion from serine 239 to methionine 309 by a glycan detection method using m ild periodate oxidation, which confirms that the sugar chain is attach ed to the conserved glycosylation site of asparagine 297. However, cha rge heterogeneity of the H chain was not entirely attributed to the Fc because the papain digest of the antibody was separated into two Fc s pots, a few Fd spots and two L chain spots by 2-D PAGE. This indicates that factors other than the sugar moiety are responsible for charge h eterogeneity of IgG monoclonal antibody. On the other hand, the H chai n isoforms of lower pi were shown to be more susceptible to V8 proteas e by peptide mapping. This result strongly suggests the occurrence of deamidation at glutamine or asparagine residues.