Abstract
We have reported previously 1 that the antibody of Type I Pneumococcus in horse or rabbit serum is separable into fractions with different immunological and physical properties and that the separation can be achieved by immunological or chemical methods. We have now found that the immunologically pure precipitin of Type I Pneumococcus is itself fractionable.
Twenty-five cc. of the antipolysaccharide precipitin solution from Type I anti-pneumococcus horse serum prepared according to our method 2 was fractionated with saturated ammonium sulphate. The scheme of fractionation and the amounts of protein obtained in each fraction are given in the diagram (Table I).
These fractions of protein were separately dissolved in water and dialyzed against pH = 5.5 acetate buffer (0.005 m) at ice-water temperature until free from sulphate. The precipitates were centrifuged and redissolved in 0.85% NaCl solution and found to be completely precipitable by the homologous polysaccharide. They represent, therefore, a fraction of the antibody with isoelectric point at pH = 5.5. The protein in the supernatant fluids was also completely precipitable by the homologous polysaccharide. The isoelectric points of these protein fractions were estimated by determination of the pH at which maximum precipitation occurred. When N/1000 HCl was added drop by drop to the supernatant fluids, precipitation of the precipitin occurred in 1 and 2 but not in 3 or 4.
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