Bull. Inst. Zool., Acadernia Sinica, Monograph 16: 37-59 (1991) STUDIES ON PISCINE GONADOTROPIN-) STRUCTURE, FUNCTION, MOLECULAR CLONING, EXPRESSION AND GENE STRUCTURE TUNG-BIN. Lo, FORE-LIEN HUANG, CHEN-SHENG LIU, YEA-SHA CHANG, GEEN-DONG CHANG and CHANG-jEN HUANG Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan 10765, Republic of China and Graduate Institute of Bioch&i-nical Sciences, National Taiwan University, Taipei, Taiwan 10765, Republic of China T. -B. Lo, F. -L. Huang, C. -S. Liu, Y. -S. Chang, G. -D. Chang and C. -J. Huang (1991) Studies on piscine gonadotropins-Structure, function, molecular cloning, expression and gene structure. Bull. Inst. Zool., Academia Sinica, Monograph 16: 37-59. Five piscine gonadotropins were isolated and purified from pituitaries of five species of fish (carp, silver carp, bighead carp, grass carp and pike eel). They are all composed of two non-identical (a and /3), non-covalently linked subunits. Each subunit is a glycoprotein and the complete amino acid sequences were determined either by the conventional chemical method or by deduction from the nucleotide sequence of the corresponding cDNA. The amino. acid sequences of a-subunit of fresh water fishes are almost identical, but show only 75% and 70% homology to marine fish and human lutropin, respectively. In j3-subunit, the similar situation are observed, i. e. almost identical between fresh water fishes, and only 80% and 46% homology to marine fish and human lutropin, respectively. The biological activity as tested both in tests of rat and carp for steroidogenesis showed distinct species specificity between mam malian lutropins and piscine gonadotropins, and j3-subuni~ was shown as the hormone specific subunit as tested by reassociated hybrid molecules. The immunological cross-reactivities of piscine and manl malian gonatropins were also corresponded to the above-mentioned species specificity. The cDNA library was constructed from corres ponding mRNA and screened either by synthetic oligonucleotide or known piscine cDNA. The nucleotide sequence of each cDNA was determined by the dideoxy nucleotide chain termination method.