Gastroenteropancreatic Hormones (Insulin, Glucagon, Somatostatin, and Multiple Forms of PYY) from the Pallid Sturgeon, Scaphirhynchus albus (Acipenseriformes)

Abstract

Insulin, glucagon, somatostatin-14, and three structurally related molecular forms of peptide tyrosine–tyrosine (PYY) were isolated from an extract of the combined pancreas and gastrointestinal tract of the pallid sturgeon, Scaphirhynchus albus. Pallid sturgeon insulin was identical to insulin from the Russian sturgeon, Acipenser guldenstaedti, and to insulin-2 from the paddlefish, Polyodon spathula, and was approximately twofold less potent than human insulin in inhibiting the binding of [3-[125I] iodotyrosine-A14] human insulin to the soluble human insulin receptor. The sturgeon glucagon (HSQGMFTNDY10-SKYLEEKLAQ20 EFVEWLKNGK30S), like the two paddlefish glucagons, contains 31 rather than 29 amino acid residues, indicative of an anomalous pathway of posttranslational processing of proglucagon. Pallid sturgeon somatostatin, identical to human somatostatin-14, was also isolated in a second molecular form containing an oxidized tryptophan residue, but [Pro2]somatostatin-14, previously isolated from the pituitary of A. guldenstaedti, was not identified. Sturgeon PYY (FPPKPEHPGD10DAPAEDVAKY20YTALRHYINL30 ITRQRY.HN2) was also isolated in variant forms containing the substitutions (Phe1 → Ala) and (Ala18 → Val), indicative of at least two gene duplications occurring within the Acipenseriformes lineage. The amino acid sequences of the pallidsturgeon PYY peptides are appreciably different from the proposed “ancestral” PYY sequence that has otherwise been very strongly conserved among the actinopterygian and elasmobranch fish.