MOUSE INSULINS — SEPARATION AND STRUCTURES

Two major components were detected by disc electrophoresis in twice crystallized mouse insulin. Gel filtration experiments indicated that the two components were two insulins rather than proinsulin and insulin. The components were separated by ion-exchange chromatography, and amino acid analysis showed both components to be insulin, differing in two amino acids. The mouse insulins were named Mouse I and Mouse II insulin by analogy with Rat I and Rat II insulin in accordance with the electrophoretic mobilities. Performic acid oxidation followed by separation of the A and B chains, and amino acid analysis of the separated chains showed both differences to be present in the B chains whereas the A chains were identical. Trypsinization of the B chains followed by separation of the tryptic peptides and amino acid analysis of the peptides yielded the following results: B 1 to B 3 were identical. B 4 to B 22 differed in one amino acid, mouse I having one proline and no serine, mouse II having one serine and no proline. Finally, free serine B 30 plus a heptapeptide (B 23-B 29) containing one lysine and no methionine was obtained from mouse I, whereas mouse II yielded an octapeptide (B 23-B 30) containing one methionine and no lysine. Mouse II insulin displayed amino acid compositions identical with those of rat II insulin in regard to the A chain, the B chain, and the tryptic peptides from the B chain.