Binding Properties of Bovine Colostral Anti-Dinitrophenyl (DNP) Immunoglobulins G2(IgG2)

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Abstract
The number of combining sites per mole of bovine colostral anti-DNP IG2 was found to be 2 and the total affinity constant was 0.81 × 104M-1 Unlike bovine colostral IgG1, the nonspecific binding of H3-−ε-DNP-1-lysine by IgG2 as a function of increased concentrations, did not show a negative, cooperative slope. Spectral measurements made with anti-DNP IgG2 in the reference cell vs. anti-DNP IgG2plus hapten in the experimental cell revealed a hypochromic, red shift from 363 to 365 nm. If the reference cell contained hapten, a red shift from 280 to 283 nm and an enhancement in the extinction coefficient of IgG2 was observed. These spectral changes were not observed if nonspecific IgG2 was substituted for anti-DNP IgG2 in the experimental cell. The enhancement in the extinction coefficient was interpreted to be due to a possible exposure of previously buried tryosine and tryptophan residues.