AMPHIBIAN LUTROPIN FROM THE BULLFROG RANA-CATESBEIANA COMPLETE AMINO-ACID-SEQUENCE OF THE BETA SUBUNIT

The amino acid sequence of lutropin (LH) beta-subunit of an amphibian, the bullfrog Rana catesbeiana, has been determined. The primary structure was determined by sequencing the intact protein (residues 1-44) and peptides originated by cyanogen bromide cleavage and lysyl endopeptidase digestion. 12 cysteine residues are conserved in the bullfrog and mammalian LH beta-subunit. One sugar-chain-binding site at Asn-8 is also conserved in the bullfrog and in all mammals except humans. This glycoprotein is composed of 112 amino acid residues with a molecular mass of 12675 Da, considering the six cystine bridges and excepting the sugar chain. The bullfrog beta-subunit has approximately 50% sequence identity with that of mammals and with the fish gonadotropin beta-subunit, and about 40% with bullfrog follicle-stimulating hormone beta-subunit.