Separation of antigens by immunological specificity. 2. Release of antigen and antibody from their complexes by aqueous carbon dioxide

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Abstract
The use of salt-free saturated aqueous carbon dioxide at pH 5 has proved to be a general method for dissociating antigen-antibody complexes. The extent of the dissociation depends on the nature of the antigen and the course of immunization used to produce the antibody. It varies between complete dissociation of antigen from antibody (a hemoglobin complex) to the liberation of a small amount of antibody from a residual insoluble complex. The salt-free environment has proved to be essential for the dissociation, and the application of aqueous carbon dioxide in such a system was a useful example of a general effect in salt-free systems produced at relatively neutral pH by a number of other acids and alkalis. A number of antibody preparations were obtained in good yield from specific precipitates after dissociation with aqueous carbon dioxide. The properties of these preparations underline the general heterogeneity of antibody as regards precipitation, solubility etc. The results are discussed in relation to the molecular forces involved in breaking the union between antigen and antibody; it is suggested that, as in other protein-protein interactions, the total antigen-antibody union is due to a complicated pattern of different interactions not all of which may have to be present for some combination to take place. This would explain the enormous variation in the strength of the antigen-antibody linkage and the heterogeneity of antibody which has been confirmed by the work described here.