The Primary Structure of Ovine Luteinizing Hormone

Abstract

Abstract The amino acid sequence of ovine luteinizing hormone β-subunit has been determined using three treatment schedules for the intact subunit to provide suitable subfractions for sequence study. In one treatment schedule cyanogen bromide cleavage, fractionation, reduction, and S-carboxymethylation was used; in a second, the tryptic peptides were isolated after digestion of reduced, S-carboxymethylated subunit. In a third procedure, the subunit was succinylated, reduced, S-carboxymethylated, and digested with trypsin. Although the third procedure blocked only 2 lysine residues to tryptic attack (positions 20 and 42) the minor cleavages by trypsin in the region of residues 27 to 42 were less troublesome and provided adequate yield of the peptides to establish this portion of the sequence. Application of the Edman degradation and COOH-terminal determinations to the peptides thus obtained allowed placement of all 119 amino acid residues of the subunit in sequence. The sequence determined in this report differs from that proposed in a brief communication by Papkoff et al. ((1971) J. Amer. Chem. Soc. 93, 1531) in the inversion of 17 amino acid residues and the placement of 1 more proline residue in their sequence. The sequence determined in the present report for ovine LH-β is in agreement with that suggested for bovine LH-β by Maghuin-Rogister and Dockier (1971) (Fed. Eur. Biochem. Soc. Lett. 19, 209) although the latter authors have 4 residues of 119 which have not been placed in sequence.