부산대학교 도서관

We have performed dielectric relaxation measurements via a time domain reflectometry (TDR) method to study dynamic behaviors of the segmental flexibility of immunoglobulin G (IgG) in aqueous solution without antigen binding. In general, an intermediate relaxation process due to bound water is observed around 100MHz at 25°C for common proteins between two relaxation processes due to overall rotation and reorientation of free water. However, the intermediate process observed around 6MHz for IgG was due to both bound water and hinge-bending motion. The apparent activation energy of 33kJ/mol was larger than 27kJ/mol for only bound water, and the relaxation strength was about five times as large as expected for bound water. The shape of the relaxation curve was very broad and asymmetric. These characteristic differences arising from the hinge-bending motion of IgG disappeared for fragments decomposed from IgG hydrolyzed by papain, since the hinge-bending motion did not exist in this case. We have separated the relaxation processes due to hinge-bending motion and bound water for IgG and obtained the Fab-Fab angle of IgG as about 130° by Kirkwood’s correlation parameter and the activation energy of 34kJ/mol for hinge-bending motion.