M.R. Sairam

Human pituitary interstitial cell stimulating hormone: Primary structure of the α subunit

Abstract The primary structure of the α subunit of human ICSH has been deduced from amino acid sequences of tryptic peptides and the compositions of cyanogen bromide fragments as well as the known structure of ovine ICSH-α. The proposed structure is shown in Figure 1. It consists of 89 amino acids with the single isoleucine residue in position 22, and the three methionine residues in positions 26, 44 and 68.

The primary structure of ovine interstitial cell-stimulating hormone: II. The β-subunit

Abstract The amino acid sequence in β-subunit of ovine ICSH has been elucidated as shown in Fig. 1. It consists of 120 amino acids with serine and leucine at the NH 2 - and COOH-termini, respectively. The single carbohydrate moiety is linked to asparagine residue at position 13.

The effects of interstitial cell-stimulating hormone, its subunits, and recombinants on isolated rat leydig cells

The stimulation of cyclic AMP accumulation and testosterone synthesis in isolated rat Leydig cells by ovine and bovine ICSH, their subunits prepared by a new, mild procedure (dissociation of subunits at pH 3 and salt fractionation) and the recombined hormones have been studied. Whereas the isolated subunits exhibit less than 0.2% of the potency of the native hormones, recombination of the subunits results in full restoration of the biological activity. In contrast to this, recombination of the subunits prepared by a countercurrent distribution method resulted in only partial regeneration of the biological activity. The ovine hormone was found to be twice as active as the bovine ICSH. Both heterologous hybrids of the subunits of the ovine and bovine hormones were significantly more active than the bovine hormone. The utility of the isolated rat Leydig cell system as a rapid, sensitive bioassay for ICSH is also discussed.

Reaction of ovine interstitial cell stimulating hormone with tetranitromethane

Abstract All the tyrosine residues of native interstitial cell stimulating hormone, and its subunits α and β, and the reassociated molecule are ionized completely at high alkaline pH. Only the ionization of the tyrosyl residues of the isolated α-subunit is completely reversible. In the native and reassociated molecules only 5 of the 7 tyrosine residues react with tetranitromethane. All 7 react in presence of guanidine hydrochloride. The tyrosine residues of the isolated α-subunit (5 residues) and β-subunit (2 residues) react completely. The unreactive tyrosines in the 5-nitro hormone derivative have been identified. Available evidence suggests that Tyr 21 of the α-subunit and Tyr 59 of the β-subunit are free and hence buried in the native hormone. Preparation of the nitro hormone derivatives with varying degrees of nitration suggests that the tyrosines of the α-subunit are the first to react with tetranitromethane. The 5-nitrohormone derivative is virtually inactive while the 1-nitro hormone derivative retains about 30% of biological activity.

Human pituitary lutropin: Isolation, properties, and the complete amino acid sequence of the β-subunit

The separation of alpha and beta subunits from human pituitary lutropin is described, and the complete amino acid sequence of the beta subunit is proposed. It consists of 115 amino acids with serine and glycine at the amino and carboxyl termini, respectively. The single carbohydrate moiety is linked to asparagine in position 30 and the single tryptophan of the lutropin molecule is located at position 8. The two methionine residues in lutropin-beta are in positions 41 and 42. In addition to COOH-terminal heterogeneity, evidence for internal peptide cleavages was observed.

Studies on the Structure and Function of Interstitial Cell-Stimulating Hormone

Publisher Summary This chapter presents studies on the structure and function of interstitial cell-stimulating hormone (ICSH). It also describes the studies on the structure of human ICSH that have led to the elucidation of the amino acid sequence of the human ICSH-α subunit. Human ICSH and ovine follicle stimulating hormone (FSH) are known to contain sialic acid. When these hormones are treated with neuraminidase to release the sialic acid, no effect is observed with regard to their lipolytic activity. The chapter also discusses in vitro stimulation of lactic acid in prepubertal rat ovaries by gonadotropins and their subunits. A number of reports have appeared in the literature that demonstrate that gonadotropins are active in stimulating lactic acid production in prepubertal rat ovaries both in vivo and in vitro.

The kinetics of dissociation and reassociation of ovine pituitary interstitial cell stimulating hormone

Abstract The dissociation of ovine interstitial cell stimulating hormone and the reassociation of its subunits have been followed by circular dichroism and sedimentation velocity measurements. The dissociation was found to be a rapid, first-order reaction accompanied by the exposure of previously buried tyrosyl groups. The reassociation reaction begins as a rapid, probably second-order formation of a complex between the α and β subunits. This is followed by a much slower, first-order rearrangement of the conformation resulting in the reburying of at least two tyrosyl groups, one contributed by each subunit.

Human pituitary thyrotropin: Isolation and chemical characterization of its subunits

Abstract The subunits of human pituitary thyrotropin have been separated and purified by countercurrent distribution and exclusion chromatography. The NH2-terminal sequence of the β subunit is identical to that of the β subunit of bovine thyrotropin. However, amino acid composition and peptide map of tryptic and chymotryptic digests as well as compositions of tryptic and chymotryptic peptides suggest that the amino acid sequence of the α subunit is identical to that of the α subunit of human interstitial cell stimulating hormone.

A simple procedure for separating the subunits of ovine and bovine pituitary interstitial cell stimulating hormone.

Abstract A simple, effective procedure for separating ovine or bovine interstitial cell stimulating hormone into their subunits has been described with a yield of 70–80%. The β subunit isolated by the new procedure behaves differently from that obtained by the countercurrent distribution method, and is in a more native state. In addition, full biological activity is consistently restored upon recombination of the subunits isolated by the new procedure.

Ovulation in Hamster: Induction by β Subunit of Ovine Interstitial Cell Stimulating Hormone

As little as 5 micrograms of interstitial cell stimulating hormone (ICSH) or 20 micrograms of ICSH-β is effective for the induction of ovulation in 100 percent of hamsters treated at 0500 hours on day 4 after lordosis, whereas as much as 800 micrograms of ICSH-α is ineffective. Both ICSH and ICSH-β are also effective for induction of ovulation in hypophysectomized animals. Thus, the ovulation-inducing activity of the ICSH molecule resides in its β subunit.