Comparative studies on thermoresistance of protein G-binding region and antigen determinant region of immunoglobulin G in acidic colostral whey

The kinetics of the denaturation of antigen determinant (AGD) region and protein G-binding (PGB) region of bovine immunoglobulin G (IgG) in acidic colostral whey were studied by single radial Immunodiffusion (SRID) and protein G affinity chromatography (PrGAC) during the same courses of heat treatment. The kinetic and thermodynamic parameters for heat-induced denaturation of AGD and PGB regions of IgG were determined over a temperature range of 69-81°C. The denaturation reactions of both AGD and PGB regions of IgG were best described with apparent reaction order of 1.2, the activation energy values of the denaturation reactions were 159.42 kJ/mol and 235.37 kJ/mol respectively. This work suggested that the AGD region was more heat-labile than the PGB region of IgG in acidic colostral whey, Moreover, the higher values of the constant for the AGD region meant that, once the unfolding of the region started, denaturation would occur more quickly than the PGB region on IgG molecule. All these factors contributed to the fact that generally the IgG contents in the products of bovine colostrum determined by PrGAC would be higher than those by SRID.