Primary structures of two forms of gonadotropin-releasing hormone, one distinct and one conserved, from catfish brain

Abstract

Two forms of gonadotropin-releasing hormone (GnRH) have been purified from brain extracts of the Thai catfish, Clarias macrocephalus, using reverse-phase high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA). The amino acid sequences of both forms of catfish GnRH (catfish GnRH-I and -II) were determined using Edman degradation. The presence of the N-terminal pGlu residue in both peptides was established by digestion with pyroglutamyl aminopeptidase. In addition, catfish GnRH-I was studied by mass spectrometry. The primary structure of catfish GnRHI is pGluHisTrpSerHisGlyLeuAsnProGlyNH2 and catfish GnRH-II is identical to chicken GnRH-II, pGluHisTrpSerHisGlyTrpTyrProGlyNH2. Functional studies showed that synthetic catfish GnRH-I released not only gonadotropin but also growth hormone from an in vitro preparation of goldfish pituitaries. Catfish GnRH-II is identical to the widely distributed and highly conserved chicken GnRH-II. Indirect evidence has suggested its presence in bony fish, but this is the first report of its primary sequence. The distinct structure of catfish GnRH-I increases the number of GnRH family members to six.