Isolation and structural characterization of insulin from the holocephalan fish, Chimaera monstrosa (rabbit fish)

Insulin has been isolated from the pancreas of the holocephalan fish, Chimaera monstrosa (rabbit fish), and characterized by automated Edman degradation and fast atom bombardment mass spectrometry. The primary structure of rabbit fish insulin was identical to that of insulin from the holocephalan fish, Hydrolagus colliei (Pacific ratfish), and contained 21 residues in the A-chain and 38 residues in the B-chain. The amino acid compositions of both rabbit fish and ratfish insulins demonstrated a value consistently lower than that expected for the leucine content of the peptides. It is suggested, therefore, that the insulins were probably isolated as a mixture of the intact peptides and components lacking the C-terminal leucine residue in the B-chain.