Primary structure of gonadotropin-releasing hormone from the brain of a holocephalan (ratfish: Hydrolagus colliei).

Gonadotropin-releasing hormone (GnRH) in the ratfish brain has been isolated and purified using reverse-phase high performance liquid chromatography. Amino acid composition and sequence analysis indicate that the primary structure is pGlu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2. The presence of the amino terminal pyroglutamic acid has been confirmed by degradation studies with pyroglutamyl aminopeptidase. The amidated carboxy terminus and molecular weight were confirmed using mass spectrometry. Moreover, sequence comparison and coelution studies with one of the synthetic forms of GnRH (chicken GnRH II) indicate that the ratfish and chicken GnRH II molecules are identical. This represents the first sequence data of a GnRH molecule from a cartilaginous fish (class: Chondrichthyes). It is argued that the ratfish GnRH molecule has been retained for over 400 million years of evolution and is expressed in most vertebrate classes.