COMPARATIVE-STUDY OF MONOCLONAL IMMUNOGLOBULIN-M AND RHEUMATOID IMMUNOGLOBULIN-M BY DIFFERENTIAL SCANNING MICROCALORIMETRY

Thermal denaturation of monoclonal immunoglobulin hi (IgM) and rheumat oid immunoglobulin M (IgM-RF) and their Fab-and (Fc)(5)-fragments was studied by differential scanning microcalorimetry. The melting of IgM- RF started at a higher temperature than that of IgM and the maximum te mperature of its main asymmetric peak of heat absorption was higher by 4 degrees C. At equal values of enthalpy, the thermal denaturation of IgM-RF and IgM consisted of four and five individual transitions, res pectively, between pairs of states. The comparison of thermal denatura tion parameters of Fab-and (Fc)(5)-fragments of IgM-RF and IgM showed a thermodynamic similarity of(Fc)S-fragments of both proteins, while t heir Fab-fragments differed in the interaction between V-L-C-L and V-H -C-H domains.