Tyrosine A14[125I]monoiodoinsulin: Preparation, Biologic Properties, and long-term stability
Abstract
125I-insulin was prepared by reacting 17.4 nmol porcine insulin (100 micrograms) with 5 mCi 125I (about 2.4 nmol) using the lactoperoxidase method. The reaction product was subjected to gel electrophoresis and the band containing A14 [125I]monoiodoinsulin was eluted. This preparation showed a specific activity of about 1.5 Ci/mumol as evaluated by radioimmunoassay and bioassay, i.e., about 75% of the theoretical maximum. The content of radioactive derivatives other than A14 monoiodoinsulin was less than 2%. The binding affinity of tracer A14 monoiodoinsulin to adipocytes, hepatocytes, and cultured human lymphocytes was twice as high as that of A19 monoiodoinsulin. Binding to antibodies was examined to 10 guinea pig anti-insulin sera. Three sera did not distinguish between the two tracers, whereas seven exhibited higher binding of the A14 tracer. A detailed analysis of one of the discriminating sera showed that the average affinity constant was about 2.5 times lower for the A19 tracer than for the A14 tracer. The A14 monoiodoinsulin tracer is remarkably stable. After 200 days the specific activity had declined to about half of its original value which is consistent with the hypothesis that the physical decay of [125I]monoiodoins...Continue Reading
Citations
Established theory of radiation-induced decay is not generalizable to Bolton-Hunter labeled peptides
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