Maturational gonadotropin from the African catfish, Clarias gariepinus: Purification, characterization, localization, and biological activity

A gonadotropic hormone of the African catfish, Clarias gariepinus, was purified and chemically characterized. Its biological activity was tested and its localization in the gonadotropic cells of the pituitary demonstrated. An ethanolic extract of 500 pituitaries of adult male and female African catfish was subjected to ion-exchange chromatography on DE-52. The 31- to 38-kDa fraction was further purified on Sephadex G-75. On rpHPLC over an ODS 120T column two major components appeared as single bands after SDS-PAGE. From the amino acid composition and sequence analysis of these fractions, compared with those of salmon and carp GTH II-α and salmon GTH II-β it was concluded that they represent catfish GTH α- and II-β-subunits. The biological activity of the complete hormone (the 31- to 38-kDa fraction from the G-75 column) was tested on the production of 11β-hydroxyandrostenedione and 17α- hydroxy-20β-dihydroprogesterone by catfish testis in vitro. Polyclonal antibodies were raised against the purified β-subunit. Immunocytochemical study using these showed them to bind specifically to hypophysial gonadotropic cells. To date only one form of GTH has been demonstrated in the African catfish.