CHARACTERIZATION OF THE 3 I-125 IODINATION ISOMERS OF HUMAN INSULIN-LIKE GROWTH-FACTOR I (IGF1)

Human insulin-like growth factor I(IGF1) was labeled with I-125 and the resulting mixture of iodination isomers was separated by reverse-phase HPLC. Three major radioactive peaks were isolated and identified by sequencing as the expected three monoiodinated species. The ranking of the affinities of the three isomers for the human IGF1 receptor was found to be Tyr(24)(I-125)>Tyr(31)(I-125)much greater than Tyr(60)(I-125). The Tyr(31)(I-125) isomer was shown to have an affinity similar to that of unlabeled IGF1 and is thus the tracer of choice for IGF1. The tracers were stable upon storage at - 20 degrees C for at least 3 months.