Primary structure of insulin of the Black Sea rockfish Scorpaena porcus

Insulin of the Black Sea rockfish Scorpaena porcus was isolated, purified, and the primary sequence has been determined. The hormone amino acid sequence has been established: the A chain-GIVEQCCNRPCNIFDLQNYCN, and the B chain--AAGPQHLCGSHLVDALYLVCGDRGFFYNPK. The rockfish insulin, in comparison with the human one, has 14 amino acid substitutions; an additional alanine is present at the N-terminal of the B-chain, whereas the 30th amino acid at the C-terminal is absent. In in vitro experiment, the 50% inhibition of the pork I-125- insulin binding to the rat liver plasma membrane was 4 nM, i.e., 50% of the standard pork insulin affinity (2 nM) to the insulin receptors. The pork rockfish insulin biological activity as determined in the mouse convulsion test in vivo was 18 +/- 2.2 ME/mg or 75% of the pork hormone activity. It is suggested that the relatively low rockfish insulin biological activity is due to the presence of A8 asparagine position in the hormone structure.