Purification and structural determination of insulins, glucagons and somatostatin from stone flounder, Kareius bicoloratus

Insulin-I and -II were purified from stone flounder (Kareius bicoloratus), and their primary structures were determined. The amino acid sequences of i nsulin-I and -II from stone flounder were identical with those of barfin fl ounder (Verasper moseri) except for position 2 of both B-chains. Insulin-II of stone flounder had an extension of the two amino acid residues (Pyr-Ala ), at the N-terminus of the B-chain. These structural characteristics of in sulins from stone flounder support the idea (Andoh and Nagasawa, Zool. Sci. 15: 931, 1998) that insulin-I and -II of flounders arise from a single pre proinsulin in each species by proteolytic cleavage at different sites of th e signal peptide region, and suggest that this generation system of two mol ecular forms of insulin is not specific for barfin flounder. In the course of the purification of insulins, somatostatin-14 and two glucagons (glucago n-I and -II) were also purified from the extract of the Brockmann body. The amino acid sequence of somatostatin-14 of stone flounder was identical wit h those of mammals. Five amino acids were different between glucagon-I and -II of stone flounder. The amino acid sequences of both glucagons were high ly conserved among several acanthopterygian and paracanthopterygian fish. T hese results suggest that their common ancestral species had both glucagons .