[Modification of the immune reaction by antigen-immunosuppressive agent-conjugates. III. Physiocochemical, antigenic and functional properties of 6-mercaptopurine coupled carrier proteins].

6-mercaptopurine (MP) conjugates of bovine gamma globulin (BGG) and human serum albumin (HSA) with increasing numbers of MP-groups per protein molecule were prepared and some physicochemical and antigenic properties studied. The electrophoretic mobility increased proportionally to the degree of substitution. In the same manner the formation of high molecular weight aggregates increased. A loss of BGG and HSA specific determinants was observed too. The physicochemical and antigenic properties of these antigen-suppressive agent-conjugates with low and medium coupling degree (to MP26-BGG and MP20-HSA) were similar to the unmodified antigens. The affinity of rabbit anti-DNP-antibodies decreased from K0 = 1,4 - 10(6) M-1 of the unmodified antibodies to 6,5 - 10(5), 3,6 - 10(5) and 3,4 - 10(5) M-1 of the antibodies conjugated with 15, 21 and 29 MP-groups per antibody molecule. The precipitation capacity of the MP-conjugated antibodies decreased to 89, 85 and 61% for the same coupling ratios. These results suggest that the upper limit of the coupling ratio of the antibodies is 20 to 1.