Primary structures of carp gonadotropin subunits deduced from cDNA nucleotide sequences

The alpha and beta subunits of carp gonadotropin (cGTH) were isolated by high performance liquid chromatography. They were identified to be the subunits of cGTH by bioassay and by partial N-terminal amino acid sequence analysis. To elucidate the complete primary structures of the alpha and beta subunits of cGTH, cDNA cloning technique was employed. The alpha and beta subunits consist of 95 and 115 amino acid residues, respectively. Homology of the alpha subunit of cGTH to those of mammalian GTH is around 70%. In comparison, the extent of homology of the beta subunit between carp and salmon GTH (75%) is higher than that between fish and mammalian GTH (39-47%). Such comparative data suggest that the alpha subunit is highly conserved while the beta subunit is diversified during the molecular evolution of vertebrate GTH.