A new insulin derivative for the preparation of insulin--enzyme conjugates: an application in the enzyme immunoassay of insulin.

A new insulin derivative, mercaptobutyrimidyl pyridine disulfide insulin, was prepared under conditions which directed the reaction preferentially through the terminal alpha-amino group of the A-chain. The purified monosubstituted insulin exhibited only a marginal decrease in antigenicity as measured by radioimmunoassay; there was, however, a significant reduction in biological activity in the mouse convulsion assay. Conjugation of the insulin derivative to human placental alkaline phosphatase was carried out via a thiol interchange reaction and the resulting conjugate was active in a double-antibody, solid-phase enzyme immunoassay for insulin.