Abstract
ULTRACENTRIFUGATION STUDIES OF DIPHTHERIA ANTITOXIN SHOWED THAT: 1. Purified antitoxin of high activity obtained from horse plasma without enzymatic treatment has exactly the same sedimentation constant as the globulin fraction obtained in a similar way from normal horse plasma s(20) (water) = 6.9 x 10(-13). 2. Purified antitoxin obtained with trypsin digestion of the toxin-antitoxin complex has a sedimentation constant of s(20) (water) = 5.5 +/- 0.1 x 10(-13), a diffusion constant of D(20) (water) = 5.7(6) x 10(-7), and a molecular weight of about 90,000. Electrophoresis experiments demonstrated that: 1. The trypsin-purified antitoxin has an isoelectric point not far from pH 7.0. 2. The reversible spreading noticed at about pH 7.3 cannot be attributed to heterogeneous preparation. 3. The large increase in the gamma-globulin fraction occurring during immunization consists either of antitoxin of various degrees of activity or of some inert protein in addition to the antitoxin.