The Reactions of Antiserum Homologous to the p-Azosuccinanilate Ion Group

It was discovered by Landsteiner and van der Scheer that the precipitation of azoprotein containing the p-azosuccinanilate ion haptenic group by hapten-homologous antiserum (anti-S_p serum) is inhibited just as well by maleate ion as by succinate ion, whereas fumarate ion is practically ineffective, and from this observation the cautious conclusion was drawn that "Accordingly, one could suppose that the succinic acid molecule can exist in a form corresponding to the cis configuration, or that the antibodies adjust themselves to this." Because of our interest in the use of immunochemical techniques for the determination of the configuration of molecules and haptenic groups, we have extended our quantitative studies of hapten inhibition of serological precipitation to include the S_p system, and have investigated the effect of over fifty haptens on the precipitation of S_p-ovalbumin and anti-S_p serum. The analysis of the data has shown that the normal configuration of the p-azosuccinanilate ion group in aqueous solution is a cis configuration, presumably stabilized by a hydrogen bond, and has provided information about the configuration of other ions.