[Partial synthesis and properties of des-A1-glycine-insulin (author's transl)]

Des-Gly-A-chain-tetra-S-sulphonate was prepared by Edman degradation following two different routes. A) Via complete reaction of A-chain from bovine insulin with 150 equivalents of phenylisothiocyanate in pyridine/water and trifluoroacetic acid cleavage of the resulting phenylthiocarbamoyl A-chain. B) Via reaction of bovine insulin with about 20 equivalents of phenylisothiocyanate until a substitution degree of 2.3-2.5 was reached, trifluoroacetic acid cleavage of the crude derivatives and oxidative sulphitolysis of the resulting desaminoacyl insulins. Preparative electrophoresis (pH 2) or ion exchange chromatography using DEAE-Sephadex gave des-Gly-A-chain in a yield of 60-65% of theory according to method B, containing less than 1% of glycine. Des-GlyA1-insulin was prepared by combination with 0.67 equivalents of B-chain-bis-S-sulphonate and isolated in yields of 5-13%, based on B-chain, after gel filtration (pH 8) and ion exchange chromatography (CM-cellulose, pH 3-2). The electrophoretically (pH 2 and 8.6) homogeneous analogue did not crystallize in the presence of zinc ions. Its blood sugar lowering potency is 10-25%, its in vitro insulin activity (fat cell assay) only 1-2%. The immunoreactivity against anti-insulin sera in different test systems is markedly reduced. There are clear differences between the CD-spectra of des-Gly-insulin and insulin, indicating a loss of ordered secondary structure. From the results it is concluded that structure-stabilizing non covalent bonds are abolished by the removal of the invariant A1-glycine. This leads to conformational alterations which cause the far-going inactivation of the molecule.