Purification, Characterization, and Bioassay of Prolactin and Growth Hormone from Temperate Basses, Genus Morone

Abstract

Prolactin (PRL) and two variants of growth hormone (GH), purified from pituitaries of striped bass (Moronesaxatilis) and its hybrid with white bass (M.saxatilis × M. chrysops) by gel filtration chromatography under alkaline conditions followed by reversed-phase high pressure liquid chromatography, appear similar between species. Both the minor (GH I) and the major (GH II) forms of purified GH appeared as single bands (Mr∼ 23,000) after sodium dodecyl sulfate–polyacrylamide gel electrophoresis, as did the purified PRL (Mr∼ 24,000). The molecular weights of GH II and PRL determined by MALDI TOF mass spectroscopy were 21.2 and 21.3 kDa, respectively. In Western blotting experiments, an antiserum against tilapia (Oreochromismossambicus) 24K PRL specifically recognized Morone PRL, while an antiserum against tilapia GH specifically recognized Morone GH I and II. Chemical identities of the putative PRL and GH I were further confirmed by N-terminal peptide sequencing, while internal sequence analysis was performed on GH II because it was blocked at its N-terminus. Over a stretch of 29 amino acids, Morone PRL was found to be 76% identical to tilapia 24K PRL, 72% identical to tilapia 20K PRL, 72% identical to chum salmon (Oncorhynchusketa) PRL I, and 69% identical to eel (Anguillajaponica) PRL I. Alignment of the hybrid striped bass GH sequences with those of several other advanced marine teleosts indicated 75–85% sequence identity for GH I (40 amino acids) and 95–98% identity for GH II (45 amino acids). Biological activity of striped bass GH II was confirmed using a heterologous invitro assay of insulin-like growth factor I mRNA production by coho salmon (On. kisutch) hepatocytes. An invivo bioassay, involving hypophysectomy of hybrid striped bass and treatment of the fish maintained in fresh water with homologous PRL, confirmed that the purified striped bass PRL was also bioactive.