Luteinizing Hormone

Abstract

Human luteinizing hormone (LH), or human lutropin as it is now called, has a molecular weight of about 32,000 (e.g. Roos et al. 1975 b); approximately 28% (w/w) of the molecule is made up of carbohydrate. (Other workers have found only about 15% carbohydrate, as cited by Roos et al. 1975 b). As is found with other glycopeptide hormones, it is composed of two dissimilar subunits each of which, alone, has little or no biological activity although 67% of the biological activity was restored when the subunits were recombined (Reichert et al. 1970). The α-subunit of human LH, comparable to the α-subunit of TSH and of follicle-stimulating hormone, contains 89 amino acids, the N-terminus coinciding with residue 8 of the α-subunit of ovine LH (which can have 96 amino acids and is identical to the α-subunit of bovine TSH). The amino acid sequences have been determined by Sairam et al. (1972) and by Shome and Parlow (1974). The β-subunit contains 115 amino acids with extensive heterogeneity at the carboxyl terminus. Seventy-five of the positions are identical with those of the β-subunit of ovine LH (e. g. Keutmann et al. 1974). The presence of 19–22 cysteine residues and 4–5 methionine residues per molecule (Roos et al. 1975 b) indicates that the molecule could have a variable three-dimensional structure. Nureddin et al. (1972) have shown that it readily undergoes some form of polymerization at certain concentrations of salts or of hydrogen ions.