Subunits of Luteinizing Hormone from Human Pituitary Glands

Abstract

Abstract Three species of luteinizing hormone (LH) designated as LH-A, -B, and -C, and containing 9, 8, and 4 NIH-LH-S1 units per mg were isolated from human pituitary glands by isoelectric focusing. The LH-A, -B, and -C each sedimented as a single boundary in the ultracentrifuge with s20,w of 2.34, 2.24, and 2.70 S, respectively. Amino acid analyses of LH-A, -B, and -C were very similar, although minor differences, whose significance remains to be determined, were observed. LH-A, -B, and -C contained 13.3, 13.2, and 6.9% of neutral sugars and 0.5, 1.3, and 1.8% of sialic acid, respectively. Minor differences in the physicochemical properties of the three forms of LH suggested microheterogeneity of the LH molecule caused by the modifications in the glycosidic linkages involving labile carbohydrate and sialic acid residues. Incubation of LH in 8 m urea followed by ion exchange chromatography on diethyl amino ethyl Sephadex A-50 resulted in the separation of α and β subunits. The α and β subunits were further purified by gel filtration on Sephadex G-100 and contained 0.8 and 1.1 units of LH activity per mg, respectively. Incubation of the α and β subunits in equal quantities (w/w) showed a 4-fold augmentation of the biological activity thus suggesting the recombination of the subunits. The gel filtration on Sephadex G-100, disc electrophoreses, amino acid analyses, and bioassays indicated that the α and β subunits of LH represent two nonidentical and noncovalently linked components of LH. The α subunits of human LH, follicle-stimulating hormone, and human chorionic gonadotropin could be substituted for each other in combination with the β subunit of each hormone suggesting that the β subunits are hormone specific and the α subunits of LH, follicle-stimulating hormone, and human chorionic gonadotropin are homologous.