[Radioligand assay: methods and application. V. Mono-125I-insulin: preparation and immunological and biological characterization]

A reproducible method for preparation of 125I-monoiodoinsulin with fully biological activity was developed. Monoiodoinsulin has been prepared from a heterogeneous 125I-iodination mixture by anion exchange chromatography on DEAE-Sephadex A-25 without using any gradient elution technique. The specific radioactivity of 125I-monoiodoinsulin was calculated to 14.3 +/- 0.8 TBq/g, i.e. an iodine content of 1.04 +/- 0.06 atoms per molecule of insulin. Monoiodoinsulin was indistinguishable from native insulin with respect to binding to guinea pig anti-insulin serum, and to insulin receptors of isolated rat adipocytes. The biological potency (96.5 +/- 7.5 per cent of the immunoreactive insulin activity) determined by the conversion of [14C1]-D-glucose to 14CO2 in vitro by rat fat cells was not significantly different from that of native insulin.