Amphibian lutropin and follitropin from the bullfrog Rana catesbeiana. Complete amino acid sequence of the alpha subunit.

The amino acid sequence of the α-subunit of the gonadotropins, lutropin and follitropin from bullfrog, Rana catesbeiana, has been determined. The α-subunit was identified in both hormones by the amino acid composition and ovulation activity of lutropin in the Xenopus ovary, by means of reconstituted hormones in various combinations. The amino acid sequences of two identical α-subunits from lutropin and follitropin were determined or deduced by different strategies. The α-subunit of those gonadotropins have 97 amino acid residues, the longest among the known α-subunits of gonadotropins, and one arginine insertion at position 29. Ten cysteine residues and two sugar-chain binding sites at Asn57 and Asn83 are completely conserved among the species. The molecular mass of this subunit is 11 026 Da not including the sugar chains. The bullfrog α-subunit has approximately 70% sequence identity with mammalian α-subunits.