Specific Hapten Binding Activity in Normal Sera

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Abstract
The successful separation of Hapten binding proteins (HBPs) from the sera of unimmunized rabbits is described. Evidence is presented indicating that each HBP is constituted of relatively homogeneous globulins which exhibit both specificity towards, and a high affinity for, the haptenic moieties to which they are directed. Electrophoresis on cellulose acetate reveals that the bulk of the protein in each of the HBPs moved in two very narrow bands and that this composition is independent of the source of the normal serum. Barbital buffer made 0.02 M p-aminobenzenesulfonate accelerates the slowest main band derived from the benzenesulfonate directed HBP, suggesting that the two main bands represent hapten dissociated and undissociated HBP. Double diffusion studies yield evidence for the presence of IgG only. There is approximately 1 μg/ml of each HBP in normal sera. We find it significant that only a single homogeneous protein represents each HBP even though the isolation was done from large serum pools.