DNA-hydrolysing activity of immunoglobulin G from bulk bovine colostrum

Abstract

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 12.2–24.1 U/mg (checked by RID) in this work. The DNase activity of bovine colostral IgG had an acidic pH optimum (pH 3.9–4.0), which was very different from the DNase (7.0–7.2) 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.