A calorimetric study of subunit interaction in immunoglobulin G

The non covalent interaction of the heavy and light chains of immuno-globulin G has been studied in a batch calorimeter and shown to be exothermic. The enthalpy of association ranged from ?5.6 to ?112.5 kJ/mole of heavy-light chain pairs formed at 25° for subunits derived from eight myeloma proteins. The values for kappa and lambda chains were not significantly different. The enthalpy showed a marked temperature dependance giving changes in heat capacity near -9kJ/deg/mole between 25° and 35° suggesting the involvement of apolar bonds in the association. However the large negative enthalpy of association suggests the presence of additional types of bonding.