A comparison of the structure of hamster pancreatic insulin and the insulin extracted from a transplantable hamster islet-cell carcinoma

Insulin has been isolated from pancreases of the Syrian hamster and from a transplantable islet-cell tumor of the hamster. Acid/ethanol extraction, ether precipitation, ion exchange and gel filtration chromatography gave preparations of suitable purity for structural studies. Using trypsin cleavage, automatic Edman degradation and manual Edman degradation, a complete sequence of the pancreatic insulin B chain was determined. By automatic Edman degradation, the amino-terminal 10 residues of the pancreatic A chain were assigned and the sequence of carboxy-terminal eleven residues could be deduced by homology to other mammalian and avian insulins. The sequence assigned to hamster insulin A chain is identical to that of the rat, mouse and spiny mouse. The sequence of hamster insulin B chain is identical to rabbit and spiny mouse B chain. In terms of protein evolution, hamster insulin thus appears to occupy an intermediate position between rabbit and rat insulins. Amino acid composition, tryptic peptide composition and partial sequence analysis of the hamster tumor insulin showed no differences from hamster pancreatic insulin.