Qualitative dissimilarities of insulin and proinsulin binding and action in vitro at IM 9-lymphocytes.

To prove hormone analogy of insulin and proinsulin 1. biochemical characterization of binding, 2. competition-inhibition-assay, 3. up-or-down-regulation, and 4. 3H-thymidine incorporation in IM 9-lymphocytes in vitro were applied. Marked differences in binding and biological activity of insulin and proinsulin in the physiological range (10 pM-1 nM) are obvious. Heterogeneity of specific insulin and proinsulin binding sites is suggested.