The effect of placement of tryptophan residues in selected A-chain positions on the biological profile of insulin.

In continuation of our efforts to study the solution structure and conformational dynamics of insulin by time-resolved fluorescence spectroscopy, we have synthesized and examined the biological activity of five insulin analogues in which selected naturally occurring residues in the A-chain have been replaced with the strongly fluorescent tryptophan residue. The potency of these analogues was evaluated in lipogenesis assays in isolated rat adipocytes, in receptor binding assays using rat liver plasma membranes, and in two cases, in receptor binding assays using adipocytes. [A3 Trp]insulin displays a potency of 3% in receptor binding assays in both liver membranes and in adipocytes, but only 0.06% in lipogenesis assays as compared to porcine insulin. [A10 Trp]insulin displays a potency of ca. 40% and ca. 25% in rat liver receptor binding and lipogenesis assays, respectively. [A13 Trp]insulin displays a potency of ca. 39% in rat liver receptor binding assays, but only ca. 9% in receptor binding in adipocytes; in lipogenesis assays, [A13 Trp]insulin displays a potency of ca. 12%, comparable to its potency in adipocyte receptor binding assays. [A15 Trp]insulin exhibits a potency of 18% and 9% in rat liver receptor binding and lipogenesis assays, respectively. The doubly substituted analogue, [A14 Trp, A19 Trp] insulin, displays a potency of ca. 0.7% in both rat liver receptor binding assays and lipogenesis assays.(ABSTRACT TRUNCATED AT 250 WORDS)