Abstract
Human insulin synthesized from A and B chains separately produced in Escherichia coli from cloned synthetic genes (prepared by the Eli Lilly Research Laboratories, Indianapolis, IN) was characterized by examining its interaction with human cultured lymphocytes, human circulating erythrocytes in vitro, and isolated rat fat cells. The binding behavior of the biosynthetic insulin with human cells was indistinguishable from that of native human or porcine insulins, with respect to affinity, association and dissociation kinetics, negative cooperativity, and the down-regulation of lymphocyte receptors. Similarly, the biosynthetic insulin was as potent as the native insulins in stimulating lipogenesis in isolated rat fat cells. We also examined the receptor binding characteristics of 125I-labeled human and porcine insulins monoiodinated solely at Tyr-A14, which were obtained by means of high-performance liquid chromatography of the iodination reaction mixture (this material was prepared by B. Frank, Eli Lilly Research Laboratories). In all aspects studied, the pure [TyrA14-125I]iodoinsulins were superior as tracers to the monoiodoinsulin purified by the more conventional method of gel filtration.