The Primary Structure of Ovine Luteinizing Hormone

Abstract

Succinylation of ovine luteinizing hormone α subunit (LH-α) and tryptic cleavage at the available arginine residues provided two fractions, only one of which contained disulfide bonds. Reduction and aminoethylation of the disulfide bonds provided two additional fractions. From these three major fractions, whose positional sequence in the original subunit could be established, the amino acid sequence for the 96 amino acid residues in the entire subunit was established. Appropriate use was made of the cyanogen bromide cleavage products and tryptic cleavage at the S-aminoethylcysteine residues, in conjunction with the Edman degradation, to establish this sequence. Determination of the NH2-terminal sequence proved difficult in view of a heterogeneity resulting from an apparent proteolytic degradation involving the first 6 residues. This sequence was ultimately clarified by a study of the cyanogen bromide cleavage peptides released after attack at the methionine in position 8. The sequence of ovine LH-α determined in the present report is identical with that for bovine thyroid-stimulating hormone α-subunit determined by Liao and Pierce (1971) J. Biol. Chem. 246, 850) and differs by a 2 residue inversion from the ovine LH-α sequence presented in a brief communication by Papkoff et. al. ((1971) J. Amer. Chem. Soc. 93, 1531).