Monoiodoinsulin specifically substituted in Tyr A14 or Tyr A19.

Monoiodoinsulin was prepared using ion exchange chromatography. The isolated monoiodoinsulin showed on polyacrylamide gel electrophoresis two bands with different intensities related to the initial method of iodination. Each of the two bands were isolated from the gel, and determination of the iodine distribution among the tyrosyl groups showed that one band contained monoiodoinsulin substituted in Try A19 contaminated with monoiodoinsulin substituted in the B-chain. The other band contained essentially A14 monoiodoinsulin. Polyacrylamide gel electrophoresis is a convenient method to prepare homogeneous A14 monoiodoinsulin with biological activity indistinguishable from that of native insulin.