Two types of light polypeptide chain (κ and λ) are present in guinea pig immunoglobulins. The ratios of K/L molecules in anti-hapten antibodies differ sometimes markedly from that found in normal serum. Anti-DNP antibodies and anti-pipsyl antibodies have, respectively, a higher and a lower than normal K/L ratio. The possibility that the L chain type affects the range of configurations which the antibody-combining site may assume was investigated. Fractional precipitation of anti-DNP antibodies from serum of guinea pigs immunized with DNP44-BSA was performed using limiting amounts of antigen. Antibody fractions were purified from each precipitate, their affinities for ϵ-DNP-L-lysine measured by fluorescence quenching (K0) and the K/L ratio estimated by precipitation with specific antisera. Increasing concentrations of L molecules were found in fractions with decreasing K0. In other experiments, fractional precipitation and purification of antibodies which cross-react with DNP was performed in serum of animals immunized with pipsyl-BGG. The K/L ratio in antibodies isolated from these fractions was much higher than in fractions which do not cross-react with DNP. These results show that K molecules are better adapted to react with the DNP hapten than L molecules. The K/L ratio in anti-DNP antibody was shown to increase in the course of immunization, at the same time that the K0 is increasing. This rise in K0 is markedly delayed when larger doses of antigen are employed.

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