(A1-phenylalanine) insulin: a new synthetic analogue.

An analogue of porcine insulin which differs from the native molecule in that the tyrosine residue in Pos. A19 is replaced by phenylalanine has been synthesized. The [PheA19]A chain was synthesized by the fragment condensation and purified as tetra-S-sulfonate by ion-exchange chromatography on DEAE-cellulose at pH 3.5. Conversion of the latter into the sulfhydryl form and combination with native sulfhydryl B chain yielded the [PheA19]insulin, which was purified by ion-exchange chromatography on CM-cellulose at pH 4.0 with an linear NaCl gradient. The biological activity of this analogue was 22.6% as measured by the rat epididymal adipocytes. It was suggested that in the insulin molecule the hydroxyl function of A19-tyrosine participates in an hydrogen-bond with the carbonyl function of A1-glycine. That hydrogen bond formation is critical for the stability of the hormone-receptor complex. The low biological activity found by us supports this hypothesis. The circular dichroism data in far UV suggest that the introduction of phenylalanine leaves the molecule structure essentially undisturbed, however the change observed in near UV could be accounted for the exchange.