Purification and characterization of insulin and peptides derived from proglucagon and prosomatostatin from the fruit-eating fish, the pacu Piaractusmesopotamicus

The fruit-eating teleost fish, the pacu Piaractus mesopotamicus (Characifor mes, Characidae) is classified along with the carp and the catfish in the s uperorder Ostariophysi. The pacu is able to survive and grow in captive con ditions feeding exclusively on carbohydrates. Hormonal polypeptides in an e xtract of pacu Brockmann bodies were purified to homogeneity by reversed ph ase HPLC and their primary structures determined by automated Edman degrada tion. Pacu insulin contains only two substitutions, Glu --> Asp at A15 and Thr --> Ser at B24 (corresponding to B22 in mammalian insulins) compared wi th carp insulin. The B-chains of both insulins contain a dipeptide extensio n to the N-terminus and a deletion of the C-terminal residue compared with human insulin. Pacu glucagon differs from catfish glucagon by a single subs titution at position 17 (Arg --> Gln. The primary structure of the 34 amino acid residue glucagon-like peptide (GLP) differs from catfish GLP only at positions 12 (Ser --> Ala) and 33 (Pro --> Gln). In common with other teleo st species, the pacu expresses two somatostatin genes. Somatostatin-14, der ived from preprosomatostatin-I (PSS-I), is identical to mammalian/catfish s omatostatin-14. Although pacu somatostatin-II was not identified in this st udy, a peptide was purified that shows 67% sequence identity with residues (1-58) of catfish preprosomatostatin-II (PSS-II). This relatively high degr ee of sequence similarity contrasts with the fact that catfish PSS-II shows virtually no sequence identity with the corresponding PSS-II from anglerfi sh (Acanthopterygii) and trout (Protoacanthopterygii). A comparison of the primary structures of the islet hormones suggest that amino acid sequences may have been better conserved within the Ostariophysi than in other groups of the taxon Euteleostei that have been studied. (C) 1999 Elsevier Science Inc. All rights reserved.