Flounder growth hormone: isolation, characterization, and effects on growth of juvenile rainbow trout

A highly purified growth hormone (GH) was isolated from the pituitary of the Japanese flounder (Paralichthys olivaceus) following extraction with alkaline solution, gel filtration on Sephadex G-75, and high-performance liquid chromatography (HPLC) on a reverse-phase column. Flounder GH (flGH) has a molecular weight of 20 kDa determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and an isoelectric point of 7.1 by gel electrofocusing. The complete amino acid sequence was determined by Edman degradation of the peptide fragments generated by enzymatic digestion and chemical cleavage. The flGH comprises 173 amino acid residues with pyroglutamate at the N-terminus. Compared with other fish GHs, flGH has an uninterrupted deletion of 14 amino acid residues near the C-terminus. flGH is the smallest of growth hormones so far reported and is a potent stimulator of growth in juvenile rainbow trout.