Single chain des-(B30) insulin. Intramolecular crosslinking of insulin by trypsin catalyzed transpeptidation

Single chain des-(B30) insulin (SCI) has been synthesized from porcine insulin by trypsin in a medium with a low content of water. Trypsin catalyzes an intramolecular transpeptidation reaction in which the glycineA1 residue substitutes the alanineB30 residue, rendering a LysB29 -GlyA1 peptide link between the A- and B-chains of insulin. The insulin derivative has been purified by column chromatography and appears to be homogeneous in HPLC and disc electrophoresis. The structure was proven to be B(1-29)-A(1-21) insulin by proteolysis with Armilliaria mellea protease followed by a few steps of Edman degradation. The electrophoretic mobility indicates that SCI has a more condensed structure than that of insulin. Perfect rhombohedral crystals were obtained under conditions resembling those under which insulin crystallizes in the same form. SCI was devoid of effect in the blood sugar lowering assay in mice, the estimated potency being less than 0.1% of that of insulin.