Isolation and Characterization of Two Distinct Gonadotropins from the Pituitary Gland of Mediterranean Yellowtail,Seriola dumerilii(Risso, 1810)

Abstract

Two gonadotropins, GTH I and GTH II, were isolated and chemically characterized from the pituitary of Mediterranean yellowtail. They were extracted with 35% ethanol–10% ammonium acetate, separated by ion-exchange chromatography on a DE-52 column, and purified by reversed-phase high-performance liquid chromatography on Asahipak C4P-50 and subsequently by gel filtration chromatography on Superdex 75. The molecular weights were estimated at 47 kDa for GTH I and 29 kDa for GTH II by SDS–PAGE and at 49 kDa for GTH I and 42 kDa for GTH II by gel filtration. GTH II was completely dissociated, while GTH I was partially dissociated into α- and β-subunits by treatment with 0.1% trifluoroacetic acid. The complete amino acid sequences of GTH α-, GTH Iβ-, and GTH IIβ-subunits were determined. The GTH α-subunit consisted of 91 amino acid residues. The GTH Iβ and GTH IIβ consisted of 105 and 115 amino acid residues, respectively, and had a 28% sequence identity to each other. They had the highest sequence identity with the respective gonadotropin subunits of bonito, tuna, and striped bass: 81–83% for GTH α, 67–71% for GTH Iβ, and 91–93% for GTH IIβ. The sequence identity of the GTH α-subunit with those of other teleosts and human and bovine LH and FSH was 57–67%. The GTH Iβ-subunit showed a low sequence identity with other known fish GTH Iβs (36–51%) and was more similar to human and bovine FSH βs (34% identity) than to human and bovine LH βs (29% identity). The sequence identity of the GTH IIβ-subunit with those of other teleosts was higher (60–73%), being more similar to LH βs (43% identity) than FSH βs (38% identity). Thus, two distinct gonadotropins, GTH I and GTH II, homologous to mammalian FSH and LH, respectively, are synthetized by M. yellowtail pituitary glands.