Separation of the subunits of ovine luteinizing hormone by a chromatographic procedure and comparison with a countercurrent distribution procedure

Regulation of RNA synthesis in corpora lutea nucleic by luteinizing hormone and derivatives

Luteinizing hormone (lutropin) stimulates glucose-6-phosphate dehydrogenase (EC 1.1.1.49) in isolated nuclei obtained from cow corpus luteum tissue. This increases the biosynthesis de novo of purine and pyrimidine nucleotides and their incorporation into RNA. RNA synthesis was measured after nuclei were incubated for 10 min in buffer media. Several reduction cleavage products and tryptic digests of lutropin inhibited the stimulatory effect of lutropin on RNA synthesis. A site of this inhibition was glucose-6-dehydrogenase.

Carboxymethylation of methionine residues in bovine pituitary luteinizing hormone and its subunits. Location of specifically modified methionine residues

Bovine lutropin (luteinizing hormone) was carboxymethylated at pH3.0 for 12 h at 37 degrees C with iodoacetic acid for specific modification of methionine residues. To facilitate the location of preferentially modified methionine residues, iodoE114C]acetic acid was added as tracer. The alpha and beta subunits of bovine lutropin were carboxymethylated with a 2- or 5-fold molar excess of iodoacetic acid either in the presence or absence of their counterpart subunits. The modified subunits were separated and isolated by counter-current distribution followed by gel filtration on Sephadex G-100. To locate the modified methiones, the isolated alpha or beta chain was reduced. S-carboxymethylated and subjected to tryptic hydrolysis. The tryptic peptides were fractionated by gel filtration on Bio-Gel P-10. From analyses of the purified 14C-labelled tryptic peptides, it was observed that methionine-8 and -33 in bovine lutropin alpha chain and methionine-52 in the beta chain were preferentially modified. Similar results were obtained when isolated alpha and beta subunits were individually carboxymethylated in the absence of their counterpart subunit under identical conditions. The fact that a recombinant of native human lutropin alpha chain, in which a valine residue is present in the position corresponding to methionine-8 of bovine lutropin alpha chain, and carboxymethylated bovine lutropin beta chain regenerated a substantial amount of receptor-site-binding activity indicated that methionine-8 in bovine alpha chain was biologically not essential. These studies showed clearly that both methionine-33 in the alpha chain and methionine-52 in the beta subunit were involved for optimum binding between bovine lutropin and its receptors for expression of hormonal activity.

Carbohydrate components of the glycopeptides of ovine lutropin

The three tryptic glycopeptides from ovine lutropin, in which two were from the alpha-subunit (alpha-56 and alpha-82 glycopeptides) and one from the beta-subunits (beta-13 glycopeptide), have been isolated and their carohydrate compositions analyzed. The results indicate that the alpha-56 glycopeptide has the highest amount of carbohydrate, whereas the beta-13 glycopeptide has the least. In general, each of the glycopeptides has similar distribution of various sugars, i.e. high in mannose and glucosamine and low in fucose, sialic acid, galactose and galactosamine. Within the limit of experimental error, the sum of their carbohydrate composition is in agreement with the published data on the intact hormone or separated subunits.