Temperature and pH dependence of immunoglobulin G conformation

Previous indirect observations have indicated that IgG may change its conformation at low or high pH and at a temperature of about 35 °C. By means of small angle neutron scattering a change in the value of the gyration radius of two different native IgG's was observed above 44 °C. No similar change was detected when the sample was previously dissolved in an acidic buffer. The acidic pretreatment caused a significant decrease in the gyration radius ( R g ) value measured at 20 °C which was partially recovered by increasing the temperature. These observations led to the assumption that the main conformational change observed appears either in the hinge region of the molecule or in the interdomain areas separating the constant and the variable domains of the Fab parts.