Synthesis of [A-2-αγ-diaminobutyric acid, A-19-glutamic acid] sheep insulin

Abstract

An analogue of sheep insulin which differs from the parent molecule in that the amino-acid residues isoleucine and tyrosine at positions 2 and 19 in the A chain are replaced by αγ-diaminobutyric acid and glutamic acid, respectively, has been synthesized. For this purpose [A₂bu²,Glu¹⁹] A chain S-suphonate was synthesized by the fragment condensation approach and isolated in purified form. Conversion of the latter into the thiol form and interaction with the S-sulphonated B chain of bovine (sheep) insulin yielded [A-A₂bu²,GIu¹⁹] sheep insulin, which was purified by chromatography on a carboxymethylcellulose column with an exponential sodium chloride gradient. This analogue, tested by the mouse convulsion assay method and in doses at least 19-fold higher than those normally used for insulin assay, was inactive. It was also inactive when tested by the radioimmunoassay method. Thus the A² and/or A¹⁹ residues must be involved in the expression of the biological activity of insulin.