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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 Á818C. 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.

Human IgG is a well-established multifunctional antigen specific immunoglobulin molecule of the adaptive immune system. However, an antigen nonspecific immunological function of human IgG has never been reported. In this study, human IgG was isolated using ammonium sulfate fractional precipitation and diethylaminoethanol (DEAE) cellulose 52 ion exchange chromatography, from which h-IgG and hs-IgG fractions were purified on the basis of their differential binding to rabbit anti-shrimp hemocyanin antibody (h) and rabbit anti-shrimp hemocyanin's small subunit antibody (hs), respectively. We found that h-IgG had a higher hemolytic activity than hs-IgG against erythrocytes from humans, rabbits, mice and chickens, whereas the control IgG showed negligible activity. h-IgG could interact directly with erythrocyte membranes, and this interaction was suppressed by high molecular weight osmoprotectants, showing that it may follow a colloid-osmotic mechanism. In comparative proteomics and glycomics studies, h-IgG and hs-IgG yielded 20 and 5 significantly altered protein spots, respectively, on a 2-D gel. The mean carbohydrate content of h-IgG and hs-IgG was approximately 3.6- and 2-fold higher than that of IgG, respectively, and the α-d-mannose/α-d-glucose content was in the order of h-IgG>hs-IgG>IgG. In this study, a novel antigen nonspecific immune property of human IgG was investigated, and the diversity in the protein constituents and glycosylation levels may have functional signficance.

This paper represents the first report of DNA-hydrolysing activity of IgG fraction from bulk bovine colostrum. Ultrafiltration, Sephadex G-150 chromatography, protein G affinity chromatography and dialysis were used to obtain the IgG fraction, which was isolated and finally purified to homogeneity by SDS-PAGE. pBR322 DNA in the incubated mixture with the IgG fraction, which was subjected to electrophoresis in 0.8% agarose gel, was found to be hydrolysed. This result was confirmed by a hyperchromicity assay using calf thymus DNA as the substrate. The DNase specific activity of the IgG preparations from bulk bovine colostrum was 12.2Á24.1 U/mg (checked by RID) in this work. The DNase activity of bovine colostral IgG had an acidic pH optimum (pH 3.9Á 4.0), which was very different from the DNase (7.0Á7.2) of the milk of healthy mothers (Kanyshkova, Buneva, Nevinsky, & Neustroev, 1997). The DNA-hydrolysing activity of bovine colostral IgG showed no significant requirement for divalent metal ions. These data taken together showed that bovine colostral IgG possessed DNA hydrolytic activity and shared biochemical properties with DNase II. We also found that the abzyme activity of IgG was not simply proportional to the IgG content.

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