Receptor Binding, Biological Activity and Immunoreactivity of (Leu^A3)-insulin, the Abnormal “Insulin Wakayama”

Abstract

The third mutant insulin (Insulin Wakayama) was proved by our group using gene technology, to be (Leu^A3)-insulin. The biological activity of insulin and its ability to bind insulin receptors extracted from the patient's serum were shown to be makedly decreased, compared with nomal human insulin. To further clarify the characteristics of the mutant insulin, semisynthesized (Leu^A3)-insulin was studied with regard to receptor binding, biological activity and immunoreactivity.
The ability of (Leu^A3)-insulin to compete with labeled human insulin for binding to isolated rat adipocytes was about 0.2% of that of the normal human insulin. The ability of (Leu^A3)-insulin to stimulate 2-deoxyglucose uptake and glucose oxidation in isolated rat adipocytes was 0.1-0.4% and 0.1-0.3% of that of the normal human insulin, respectively.
The biological activity of (Leu^A3)-insulin was additive to the normal human insulin. (Leu^A3)-insulin demonstrated a decreased immunoreactivity with anti-insulin antibodies.
These findings indicate that A-chain 3 valine residue is very important for the active biological function of the insulin molecule and also plays an essential role in binding to anti-insulin antibodies.