Immunoelectrophoretic characterization of insulin monomers and polymers

Insulin monomers and polymers were analysed by quantitative immunoelectrophoretic procedures. The Zn-insulin hexamer dissociated reversibly by dialysis against the Zn-free electrophoresis buffer. The Zn-insulin polymers showed precipitin reactions of partial identity. Monomeric salt-free insulin migrated as soluble immune complexes in the antiserum gel. The insulin monomer did not absorb the precipitating antibodies against the Zn-insulin polymers. Thus the polymer structure creates antigenic epitopes absent from the insulin monomer. As insulin is probably released from the beta cells in the relatively stable form of Zn-insulin hexamers, selective monomer assays might underestimate the total content of immunoreactive insulin in the biological fluids. Electroimmunoassay of Zn-insulin immunoreactive antigens in human urine defines a normal reference range of 10-25 ng/ml.