The optical rotatory dispersion of antigen-antibody complexes.

The optical rotations of solutions of the antigen—antibody complexes formed by excess of antigen were measured over a range of wave-lengths. The antigens used were bovine serum albumin (BSA) and diphtheria toxin. A method of estimating the optical rotations of the precipitable antibody against BSA in a solution of rabbit γG-globulin was used. The antitoxin used was isolated peptic antitoxin. The optical rotations found were compared with those anticipated if the optical rotations had not been altered on combination. The optical rotation of the BSA—antibody complex at the D-line did not differ appreciably from that anticipated, but differences were found at shorter wave-lengths. Mixtures of toxin and peptic antitoxin, in which the molecular ratios of toxin to antitoxin ranged from 2.29 to 0.37, gave rotatory dispersion curves, in the far ultraviolet range, which differed from those of the sums of the separate specific rotations of the constituent toxin, free and combined, and antitoxin. The differences in position and amplitude of peaks and troughs depended on the ratio of toxin to antitoxin. But in every mixture the maximum specific rotation at 205–210 mμ was less than the anticipated maximum rotation. Over the range 230–250 mμ the observed specific rotations of the mixture in which the ratio of toxin to antitoxin was highest were less negative than the anticipated specific rotations; in the mixture in which the ratio of toxin to antitoxin was lowest the observed rotations over the range 225–400 mμ were more negative than those anticipated.