A method for the preparation of protein-protein conjugates of predetermined composition.

A novel procedure for the synthesis of well-defined protein-protein conjugates is described using ovalbumin (OA) and IgG as test proteins. This procedure involves the highly selective and rapid reaction of alkyl halide and sulfhydryl groups, which have been grafted, respectively, onto the proteins to be conjugated. Accordingly, iodoacetylated IgG, (ICH2CO)nIgG, was prepared by the reaction of the epsilon-amino groups of IgG with the N-hydroxysuccinimide ester of iodoacetic acid (NHIA), the degree of iodoacetylation (n) being proportional to the concentration of NHIA. OA was reacted with S-acetylmercaptosuccinic anhydride (SAMSA) under conditions yielding, on the average, a monosubstituted derivative. Following removal of the protective S-acetyl group, the resulting -SH derivative of OA was reacted with (ICH2CO)nIgG. The OAx-IgG conjugates so produced were characterized by gel filtration, specific radioactivity (using tritiated OA) and immunodiffusion. It was found that the average number of OA molecules coupled per IgG molecule could be controlled by varying the degree of iodoacetylation of IgG.