Isolation, structure, and synthesis of a human seminal plasma peptide with inhibin-like activity

Identification of novel semenogelin I-derived antimicrobial peptide from liquefied human seminal plasma

Semenogelin I (SgI) is one of the most abundant proteins in human seminal plasma. SgI plays a key role in sperm coagulation and spermatozoon immobilization. In addition, SgI and/or its proteolytic fragments are involved in regulating spermatozoon motility, capacitation and inhibin-like activity. However, little is known about the antibacterial activity of SgI-derived peptides. By a combination of ion-exchange, gel filtration and high-performance liquid chromatography, peptides from liquefied human seminal plasma from 40 healthy donors were isolated and characterized. N-terminal amino-acid sequencing and fast atom bombardment mass spectrometry revealed that four isolated peptides were SgI-derived, namely SgI-29 (85-113), SgI-46 (85-130), SgI-47 (85-131) and SgI-52 (85-136). Interestingly, SgI-29, SgI-46 and SgI-47 are newly identified SgI-derived peptides. Antimicrobial activity assay results indicated that synthesized SgI-29 had strong antibacterial activity toward various bacterial strains. Our results indicate that SgI can be digested into small fragments like newly identified SgI-29, SgI-46 and SgI-47 and may have diversified functions.

Involvement of Semenogelin-Derived Peptides in the Antibacterial Activity of Human Seminal Plasma1

Mechanisms for protecting spermatozoa, and the testes that produce them, from infection are essential, given the importance of these cells and organs for the fertility of the individual and perpetuation of the species. This is borne out by the publication of numerous papers on this subject over the last 50 years. We extended our work and that of others on the anti-infectious defense system of the male genital tract, using a new strategy for the direct identification of antibacterial molecules in human seminal plasma. We subjected a liquefied seminal plasma cationic fraction to reversed-phase HPLC, monitored microbicidal activity by gel overlay and radial diffusion assays, and identified the proteins and/or peptides present in each active fraction by mass spectrometry. In addition to proteins with known potent microbicidal activity--phospholipase A2, lactoferrin, and lysozyme--we also found that peptides produced by cleavage of semenogelin I, the predominant human semen coagulum protein, had high levels of antibacterial activity.

Fluoride-induced disruption of reproductive hormones in men

Fluoride-induced reproductive effects have been reported in experimental models and in humans. However, these effects were found in heavily exposed scenarios. Therefore, in this work our objective was to study reproductive parameters in a population exposed to fluoride at doses of 3-27 mg/day (high-fluoride-exposed group-HFEG). Urinary fluoride levels, semen parameters, and reproductive hormones in serum (LH, FSH, estradiol, prolactin, inhibin-B, free and total testosterone) were measured. Results were compared with a group of individuals exposed to fluoride at lower doses: 2-13 mg/day (low-fluoride-exposed group-LFEG). A significant increase in FSH (P<0.05) and a reduction of inhibin-B, free testosterone, and prolactin in serum (P<0.05) were noticed in the HFEG. When HFEG was compared to LFEG, a decreased sensitivity was found in the FSH response to inhibin-B (P<0.05). A significant negative partial correlation was observed between urinary fluoride and serum levels of inhibin-B (r=-0.333, P=0.028) in LFEG. Furthermore, a significant partial correlation was observed between a chronic exposure index for fluoride and the serum concentrations of inhibin-B (r=-0.163, P=0.037) in HFEG. No abnormalities were found in the semen parameters studied in the present work, neither in the HFEG, nor in the LFEG. The results obtained indicate that a fluoride exposure of 3-27 mg/day induces a subclinical reproductive effect that can be explained by a fluoride-induced toxic effect in both Sertoli cells and gonadotrophs.

Progesterone induced modulations of serum hormonal profiles in adult male and female rats

The impact of progesterone on serum hormonal profiles in the presence and absence of gonads was studied in adult male and female albino rats. Progesterone was administered intramuscularly for 30 days at a dose of 1 mg/100g body weight/day. Serum testosterone, estradiol and prolactin titres decreased in male and female rats with intact gonads given progesterone. While the levels of both luteinizing hormone (LH) and follicle stimulating hormone (FSH) decreased in male rats with intact gonads, only FSH decreased in female rats. The inhibitory effect of progesterone on serum estradiol, LH, FSH and prolactin persisted even after gonadectomy in male rats. This persistent inhibitory effect of progesterone was also seen on serum testosterone, FSH and prolactin levels of female rats. Ovariectomy modified progesterone action on LH, as is evident from the decreased levels of LH observed only in ovariectomized rats given progesterone. While progesterone had no effect on serum T3 and T4 in male rats, gonadectomy altered the levels of T3 and T4 in male and female rats. Progesterone increased the levels of T3 and decreased the levels of T4 in ovariectomized rats. Growth hormone (GH) and thyroid stimulating hormone (TSH) levels seem to be resistant to changes in progesterone titre, irrespective of the sex and gonadal status. The present data suggest the existence of a sex specific effect of progesterone on gonadotrophins. The data on T3, T4 and TSH reveals that progesterone has no effect on the pituitary thyroid axis in the presence of gonads.

Inhibins, activins, and follistatins: expression of mRNAs and cellular localization in tissues from men with benign prostatic hyperplasia

BACKGROUND

The transforming growth factor beta (TGF beta) superfamily of growth factors includes activins and inhibins, which have been shown to be present in the rat ventral prostate, and human prostate tumor cell lines, although their localization in benign prostatic hyperplasia (BPH) tissue is currently unknown.

METHODS

BPH tissues were obtained at surgery, and the mRNA expression for the inhibin alpha, beta A, beta B subunits, the putative activin beta C subunit, the activin type II receptor (ActRII), and the activin binding protein, follistatin, was determined by reverse transcription polymerase chain reaction (RT-PCR) and Southern blot analysis. Antibodies specific for alpha, beta A, beta B, activin A, and follistatin were used to determine the localization of these proteins in BPH tissue specimens.

RESULTS

Southern blot analysis confirmed that mRNA for ActRII, beta C subunit, and follistatin was present in all biopsy samples assayed. However, alpha, beta A, and beta B subunit mRNA expression was variable between patient samples. Immunohistochemistry demonstrated the predominant localization of beta A, beta B, and activin A proteins to the epithelium of BPH tissues. No immunoreactivity for the inhibin alpha subunit was detected; follistatin immunoreactivity was localized to the fibroblastic stroma.

CONCLUSIONS

The compartmentalization of activin subunit proteins to the epithelium, and of follistatin to the stroma, suggests that a paracrine interaction occurs between the activin ligands and follistatin-binding proteins in BPH tissue.

Peptide chemistry: development of high performance liquid chromatography and capillary zone electrophoresis

The development of relatively non-compressible supporting media of small particle size as well as pumps that deliver constant flow rates at high pressures has enabled investigators to perform rapid, high resolution liquid chromatography for more than two decades. Studies initiated in this laboratory in 1975, evaluating the compatibility of unprotected peptides with commercially available chromatographic supports and development of solvent systems ultimately led to separations not previously observed with both synthetic peptides and native peptides from tissue extracts. It was rapidly realized however, that recovery of certain molecules could be problematic. To meet the challenges presented by the isolation of natural hormones (such as corticotropin releasing factor and growth hormone releasing hormone) and proteins (such as inhibin and activin) and the need for large quantities of highly purified peptides for clinical investigations, our group invested heavily in identifying new supports (high carbon loading and 300 A pore sizes) and solvent systems (triethylammonium phosphate and trifluoroacetic acid) compatible with reverse phase, size exclusion and ion exchange chromatographies from a practical and economical perspective. More recently, we have contributed to the identification of unusual buffer systems (inclusive of organic modifiers) compatible with capillary zone electrophoresis that will both modulate the capillaries' selectivity, increase resolution and serve as an orthogonal approach to determining peptide purity. From a pragmatic point of view, in this paper we highlight the original and timely contributions (technical and strategical) of this laboratory in the field of analytical and preparative high performance liquid chromatography and capillary zone electrophoresis of synthetic and native biologically active peptides and proteins over the past twenty years.

Effects of alpha-inhibin-92 fragments and alpha-inhibin-92 antiserum on the control of follicle-stimulating hormone release in male rats

Alpha-inhibin-92 (alpha-IB-92) has been characterized from human seminal plasma and found to be active in suppressing FSH release in vitro and in vivo. In order to determine if smaller fragments of this 92 amino acid peptide would still be active to suppress FSH release, we have evaluated 5 of these fragments for their effects on FSH and LH release in the present study. Five alpha-IB-92 fragments (1-34, 1-46, 35-65, 35-92 and 66-92) were synthesized and injected intravenously (iv) into castrated adult rats (2 days post operation). Only fragments alpha-IB-92-(35-65) and alpha-IB-92-(66-92) significantly lowered plasma FSH, but not LH, at doses of 10 micrograms. These fragments exerted a preferential FSH-suppressing effect, but their activities were less than that of alpha-IB-92. In view of the rapid action of these peptides and the preferential FSH suppressing effect, they could be useful clinically to suppress FSH release. To determine the possible physiologic significance of alpha-IB-92, we injected antiserum raised against alpha-IB-92 into immature male rats and evaluated its effects on FSH and LH release. Normal rabbit serum (NRS) or anti-alpha-IB-92 serum was injected iv through indwelling jugular catheters into conscious, unrestrained 18 day-old male rats. Blood samples (0.2 ml) were collected at various intervals. Intravenous injection of alpha-IB-92 antiserum (0.1 ml/rat) selectively elevated plasma levels of FSH but not LH from 2-8 h post-injection in 18 day-old male rats (P < 0.01). Since immunoneutralization of alpha-IB-92 significantly elevated FSH release in immature rats, alpha-IB-92 has a physiological inhibiting role in control of FSH but not LH release at this stage of development.

Inhibition of DNA polymerization and DNA transcription to RNA by seminal plasma peptides

An oligopeptide fraction purified from the extracellular compartment of bull semen and strongly interacting with DNA was shown to hinder mononucleotide polymerizations to DNA and RNA in vitro. The fraction, collectively called seminal plasma inhibitor, was active in the endogenous DNA and RNA polymerase reactions of the nuclei from rat hepatocytes and in the analogous nucleotide polymerizations catalyzed by purified enzymes of bacterial origin. The type of the induced inhibition was studied using the RNA polymerase from Escherichia coli as a representative nucleotidyl transferase. In the enzymatic polycondensation of mononucleotides, the seminal plasma inhibitor appeared to exert its effect mainly by a competitive inhibition for the utilization of DNA templates without specificity with respect to the source and the base sequence of DNA. Concavities of the plots of V0/Vi versus the amounts of inhibitor in the nucleotide polymerizing reactions and of the Dixon plots in the assays of RNA polymerase from E. coli suggested that the isolated oligopeptide fraction contained more than one active molecular species with differential effects at low and high doses. Preliminary results on the microheterogeneity of the seminal plasma inhibitor supported this contention.

Synthetic human seminal alpha-inhibin-92 selectively suppresses follicle-stimulating hormone release in vivo

A 92-amino acid polypeptide, alpha-inhibin-92 (alpha-IB-92), has been isolated and characterized from human seminal plasma and found to be active in suppressing follicle-stimulating hormone (FSH) release in vitro. In the present in vivo study, intravenous injection of synthetic alpha-IB-92 (4 and 20 micrograms) significantly suppressed FSH release (P less than 0.001), whereas this peptide had no effect on luteinizing hormone (LH) release in 1-day orchidectomized male rats. In contrast, third ventricular injection of alpha-IB-92 (0.02, 0.4, 4, or 20 micrograms) had no effect on FSH and LH release in 1- or 2-day orchidectomized rats. These results indicate that alpha-IB-92 exerts a FSH suppressing activity by direct action on the pituitary gland.

Characteristics of binding of human seminal alpha-inhibin-92 to human pituitary membranes

We investigated the binding of 125I-labeled alpha-inhibin-92 (a 92-residue peptide) to human pituitary membrane preparations. Unlabeled alpha-inhibin-92 competed effectively with the labeled peptide for binding to the membranes. Binding was also inhibited by both alpha-inhibin-52 and alpha-inhibin-31, but less effectively. Scatchard analysis of the alpha-inhibin-92 binding data indicated the presence of high-affinity binding sites (1.35 nM/mg of membrane protein) with an apparent Kd of 0.37 nM. When 125I-labeled alpha-inhibin-92 was covalently crosslinked to the pituitary membrane preparation with disuccinimidyl suberate and the solubilized labeled receptor complex was analyzed by NaDodSO4/PAGE under either reducing or nonreducing conditions, a single radioactive band at an apparent molecular weight of 90,000 +/- 5000 was observed. These data suggest that human pituitary has specific binding sites for alpha-inhibins.

Localization of alpha-inhibin-31 in rodent testis and brain by immunocytochemical procedure and Western blot analysis

Using an anti-serum against synthetic alpha-inhibin-31, we have studied its cellular locations in rodent testis and brain. Western blot analysis detected several molecular forms of the protein(s). A protein of 17 KDa in size was detected in testis of one month old mice. Two major bands of molecular weights 39 kDA and 21 kDA were detected in mature mouse testis. The 39 kDA protein was also present in male brain, female brain and ovary. No protein similar in size to alpha-inhibin-31 was detected with this antiserum, suggesting that the antibody recognized only the precursor of the alpha-IB-31 molecule. Immunocytochemical studies revealed that these molecules were located in the cytoplasm of the interstitial Leydig cells. The immunocytochemical reaction can be eliminated by pre-incubation with synthetic alpha-inhibin-31. Immunoreactive substances were also demonstrated at the blood-brain barrier on the external surface of the ependymal cells in the third ventricle of the rat brain. In the pituitary, similar pattern of localization was also observed in the cuboidal-columnar epithelial cells that lined the par tuberalis between the anterior and intermediate lobes. The immunoreaction to the neural cells cannot be completely abolished by competition with the synthetic peptide. These observations suggested that alpha-inhibins are located in the Leydig cells of the testis as well as in the brain, pituitary and ovary.

Synthetic peptide with inhibin-like activity preferentially inhibits follitropin secretion in comparison with lutropin-releasing hormone antagonists

Biological activity of a synthetic peptide with inhibin-like activity under in vitro and in vivo conditions was compared with three highly potent synthetic lutropin-releasing hormone antagonists. Unlike the synthetic lutropin-releasing hormone antagonists, which effectively inhibited both lutropin and follitropin secretion from the pituitary, the inhibin-like peptide showed a preferential effect by inhibiting follitropin release both in vitro and in vivo. Thus, small peptides such as inhibin-like peptide with a sequence unrelated to lutropin-releasing hormone may provide a basis for design of selective inhibitors of gonadotropin release.

Antibodies to human seminal plasma inhibin cause sperm agglutination and impairment of cervical mucus penetration and sperm-egg attachment

Inhibin isolated from human seminal plasma which has 94 amino acids has been shown to be structurally similar to a sperm coating antigen of prostatic origin. Specific antibodies generated against this peptide caused agglutination of human sperm. Using FITC-labeled antibody, antigen was localized on the post-acrosomal head region of sperm. Antiserum to inhibin could also impair the penetration of human spermatozoa into cervical mucus. After 10 and 30 minutes, the depth and density of penetration as well as the motility of the sperm were inhibited. The treatment of sperm with antiserum to inhibin caused an inhibition of sperm attachment to the egg as well as inhibition of penetration.

Inhibin--a non-steroidal regulator of pituitary follicle stimulating hormone

Inhibin is a gonadal glycoprotein produced by the granulosa and Sertoli cell under the influence of FSH and acts to specifically suppress pituitary FSH secretion. Recently, ovarian inhibin has been purified from several species and its amino acid sequence deduced using cloning techniques. Inhibin consists of two disulphide-linked heterologous subunits of which the smaller may exist in two different forms accounting for two different forms of inhibin in humans and pigs. Heterogeneity of inhibin also exists as a result of proteolytic processing of the molecule during its passage into the circulation. Significant homology exists between the subunits of inhibin and the dimeric peptides TGF-beta and Mullerian inhibitory substance (MIS), suggesting they are all derived from a common ancestral gene. Furthermore, dimers of the smaller subunit of inhibin (FSH-releasing protein (FRP) or activin) have now been found in follicular fluid (FF) and, along with TGF-beta, shown to be potent and specific stimulators of FSH secretion. These proteins may be involved in controlling FSH by another as yet unknown pathway and may prove to be the FSH-releasing factor, analogous to LHRH, which has been postulated to exist for some years. Inhibin can no longer be simply considered as an isolated FSH-suppressing protein. The physiological significance and relationship between inhibin and its related proteins represent one of the most challenging and interesting areas in reproductive endocrinology. Further studies, particularly with the development and use of sensitive assays for both the FSH releasing hormone and inhibin will clarify their role in reproduction and their usefulness in monitoring or treating fertility.

Hormonal regulation of inhibin production by cultured Sertoli cells

The hormonal regulation of inhibin production by cultured rat Sertoli cells was examined using a specific radioimmunoassay (RIA) which detects the N-terminal portion of the porcine inhibin alpha chain. FSH, but not hCG or prolactin caused a dose-dependent increase in inhibin production (EC50 for FSH = 2.4 ng/ml); both secreted and intracellular levels of inhibin were increased, but the secreted form represented one-half to two-thirds of the total. The FSH-stimulated production of inhibin was augmented by addition of a phosphodiesterase inhibitor, and could be mimicked by cholera toxin, forskolin, or dibutyryl cAMP, all of which are known to increase intracellular cAMP levels. Inclusion of either dihydrotestosterone or estradiol in the cultures had no effect on inhibin production, both in the presence and absence of FSH. Examination of the conditioned media from forskolin-treated Sertoli cells by gel filtration chromatography revealed a single peak of bioactive and immunoreactive inhibin, at a molecular weight of approximately 32,000, similar to that observed for the porcine and bovine follicular fluid inhibins. Thus, FSH activated the cAMP pathway to stimulate Sertoli cell production of inhibin which in turn suppresses pituitary FSH release to form a closed-loop feedback system.

Chemical synthesis of alpha-inhibin-92 by the thiocarboxyl segment coupling method

The amino acid residue peptide, alpha-inhibin-92 (alpha-IB-92), has been synthesized by the thiocarboxyl segment strategy. Three segments were synthesized by the solid phase method, purified, and characterized: [GlyS34]-alpha-IB-92-(1-34) (I), CF3CO-[GlyS65]-alpha-IB-92-(35-65) (II), and Msc-alpha-IB-92-(66-92) (III). All were reacted with citraconic anhydride followed by removal of the Msc group in III to give Ia, IIa, and IIIa, respectively. Peptide IIIa was coupled to IIa by the silver nitrate/N-hydroxysuccinimide procedure and, after removal of uncoupled segments and the trifluoroacetyl group, Ia was coupled followed again by removal of uncoupled segments. Final deblocking to remove citraconyl groups was accomplished under exceptionally mild conditions in aqueous acetic acid. The synthetic product was identical to natural alpha-IB-92 in amino acid analysis, HPLC, gel electrophoresis, and tryptic mapping. The synthetic peptide was indistinguishable from natural alpha-IB-92 in a radioimmunoassay and in an in vitro mouse pituitary assay for measuring suppression of FSH release in the presence of LHRH.

Superoxide dismutase in human testis preparations

A protein fraction from human testis was structurally investigated. The main component of the fraction reported to contain inhibin-like activity was purified and analyzed by tryptic digestion. The peptides obtained identified the protein as an enzyme, superoxide dismutase, previously known to be present in seminal plasma. The results show that superoxide dismutase is a major enzyme, also of testicular material. They further demonstrate the importance of using pure fractions, and controls such as checks with structural analysis or synthetic peptides, in the work of elucidating the nature of inhibin and other hormonal peptides.

Molecular structure of human seminal coagulum: the role of proteolysis

The techniques of SDS-polyacrylamide slab gel electrophoresis and a sensitive fluorescamine-based method were used to study autoproteolysis of human seminal coagulum at various pH. The major protein bands of 72 and 55 Kd were optimally degraded at pH 7.5. Degradation at pH 3.5 was preceded by a lag period of 30 min. When the seminal coagulum was incubated for 5 min at pH 7.5 and then adjusted to pH 3.5, degradation was more rapid and complete than at pH 3.5 only. Autoproteolytic degradation product of discreted sizes were obtained when compared with degradation in the presence of pronase.

Human seminal alpha-inhibins: detection in human pituitary, hypothalamus, and serum by immunoreactivity

An antiserum generated in rabbits against human seminal alpha-inhibin-52 has been used to develop a sensitive radioimmunoassay for the detection of alpha-inhibins. The alpha-inhibin-52 antiserum reacts with alpha-inhibin-92 and alpha-inhibin-31 with equal avidity. These peptides were found to be present in human pituitary, hypothalamus, and serum. In exclusion chromatography on Sephadex G-100, the immunoreactive material eluted in a large molecular size region. Immunoblot analysis of column-derived fractions of these extracts revealed the presence of alpha-inhibin-92. The mean concentrations of immunoreactive alpha-inhibin were found to be 7.2 ng/ml in normal adult male serum, 70.3 ng/g (wet weight) of pituitary, and 12.9 ng/g (wet weight) of hypothalamus. This communication reports on the evidence for the existence of gonadal peptides in the brain.

Peptides of postulated inhibin activity. Lack of in vitro inhibin activity of a 94-residue peptide isolated from human seminal plasma, and of a synthetic replicate of its C-terminal 28-residue segment

A 94-residue polypeptide isolated from human seminal plasma and its chemically synthesized C-terminal 28-residue segment were studied in an in vitro inhibin bioassay utilizing rat pituitary cell cultures. Both peptides have previously been claimed to have inhibin activities, and the effects on the secretion and cellular content of gonadotrophins (FSH and LH) were now assessed in the in vitro assay. No inhibition was found. After 72 h of culture, both the cellular content and the spontaneous as well as the LHRH-stimulated release of bioactive or immunoactive FSH and LH remained unaffected. Similarly, no effects were found on the storage and/or release of prolactin, growth hormone, or thyrotropin. We conclude that both the native 94-residue peptide and the synthetic replicate of its C-terminal 28-residue segment, do not influence the pituitary FSH secretion when assessed in this in vitro system.

Isolation of bovine follicular fluid inhibin of about 32 kDa

Inhibin of about 32 kDa from bovine follicular fluid (bFF) was purified by using chromatographies operated under protein-dissociating conditions, which we have established for our previous purification of porcine follicular fluid (pFF) inhibin. On a gel filtration, bFF inhibin activity was eluted at 3 distinct regions corresponding to apparent molecular weight of 96, 55 and 32 kDa, representing 17%, 27% and 24% of the total inhibin activity in the follicular fluid, respectively. The smallest inhibin, named 32 kDa bFF inhibin, that evidently suppressed the basal secretion of FSH from the pituitary cells, was purified to homogeneity with a 5330-fold purification factor in a recovery yield of ca. 11%. 32 kDa bFF inhibin thus purified consists of 2 polypeptide chains (A-chain: 20 kDa and B-chain: 13 kDa), linked by disulfide bridges. N-Terminal sequences were Ser-Thr-Pro-Pro- for the A-chain and Gly-Leu-Glu-Cys- for the B-chain. The identical N-terminal sequences were also found in 32 kDa pFF inhibin, except that Pro-3 of the bFF A-chain is substituted by Ala in the 20 kDa chain of pFF inhibin.

Complementary DNA sequences of ovarian follicular fluid inhibin show precursor structure and homology with transforming growth factor-beta

Inhibin, a specific and potent polypeptide inhibitor of the secretion of follicle-stimulating hormone (FSH), of gonadal origin and thus a potential contraceptive, may constitute a missing link in the mechanism controlling the differential secretion of the pituitary gonadotropins. Inhibin-like bioactivity has been reported in various fluids and extracts of testis and in ovarian follicular fluid. Although there have been several attempts to purify inhibin from seminal plasma, purification from follicular fluid has been more successful (refs 14-16; for review see ref. 17). We have previously isolated two forms (A and B) of inhibin from porcine follicular fluid. Each form comprised two dissimilar subunits of relative molecular mass (Mr) 18,000 (18K, referred to here as the alpha-subunit) and 14K (the beta-subunit), crosslinked by one or more disulphide bridge(s). Forms A and B differ in the N-terminal sequence of their 14K subunit. Preliminary structural characterization of porcine and bovine ovarian inhibins shows that they have similar properties. Here, we have used the N-terminal amino-acid sequence data on the subunits of each inhibin to identify cloned complementary DNAs encoding the biosynthetic precursors and report that inhibins are the product of a gene family that also includes transforming growth factor-beta (TGF-beta) and whose structural organization is similar to that of pituitary and placental glycoprotein hormones.

Isolation and partial characterization of a Mr 32,000 protein with inhibin activity from porcine follicular fluid

A Mr 32,000 protein with inhibin activity was isolated from porcine follicular fluid by heparin-Sepharose affinity chromatography, gel filtration on Sephacryl S-200, and four reversed-phase HPLC steps. The isolated molecule is composed of two chains having molecular weights of 18,000 and 14,000, respectively, and bound together by disulfide bonds. Amino acid sequence analysis revealed the 10 NH2-terminal residues of the Mr 18,000 chain to be Ser-Thr-Ala-Pro-Leu-Pro-Trp-Pro-Trp-Ser- and those of the Mr 14,000 chain to be Gly-Leu-Glu-Xaa-Asp-Gly-Arg-Thr-Asn-Leu-. This Mr 32,000 protein specifically inhibits the basal secretion of FSH, but not that of LH, in the rat anterior pituitary monolayer culture system, with a half-maximal effective dose of 450 pg/ml.

Comparison between inhibin from human and bovine ovarian follicular fluid using fast protein liquid chromatography

Inhibin from human and bovine ovarian follicular fluid was purified 700-900-fold using affinity chromatography on immobilized Procion Red 3B, desalting on Sephadex G-25, ion-exchange chromatography on the fast protein liquid chromatography (FPLC) columns Mono Q and Mono P and chromatography on immobilized lectins. Isoelectric points for inhibin from human and bovine origin were between 5.1-5.7 and 4.75-5.25, respectively. Inhibin from both sources was retained by immobilized lectins, indicating its association with a glycoprotein. Overall recoveries of inhibin activity after these chromatographic procedures were approximately 1%.

Inhibin: 1985 update on action and purification

Inhibin is a gonadal hormone, which exerts a specific negative feedback action on the pituitary secretion of follitropin (FSH) in male and female animals. The existence of inhibin was postulated over 60 years ago. Yet, until recently, little progress has been made in its isolation and characterisation. This lack of progress may be attributed to several factors: first, the use of a variety of assay systems of ill-defined specificity, secondly, the use of a variety of sources for unpurified inhibin, and thirdly, the inability of investigators to purify inhibin using classical purification procedures. During the last few years, and in particular during the last year, several publications on the isolation and characterisation of inhibin have appeared. This review attempts to place the various reports on the nature of inhibin into perspective. It is concluded that there are at least 2 classes of proteins with inhibin-like activity: a relatively large molecular weight material with apparent molecular mass between 40 and 70 kDa found in gonadal extracts and fluids, and a smaller material, with molecular mass between 5 and 20 kDa, found in seminal plasma. However, the observations that various purified seminal plasma inhibin preparations are either inactive in in vitro assays used to characterize gonadal inhibin or have been shown to be prostatic in origin suggest that they are unlikely to be involved in the gonadal regulation of FSH secretion. It has yet to be established if the purified gonadal inhibin preparations are the biological active forms involved in controlling FSH secretion in vivo.

On the identity of bovine seminal plasma inhibin

In light of current discussions on multiple forms of inhibin, it was thought of interest to ascertain the identity of the postulated 'iso-hormones' of bull seminal plasma inhibin (Chari et al., 1978). By subjecting the biologically active fraction, obtained by Sephadex G-100 gel filtration of bull seminal plasma acetone powder, to extensive dialysis in distilled water adjusted to pH 5.8, it was possible to remove the bulk of inert protein as a precipitate. The resulting active preparation could be readily fractionated by preparative iso-electric focusing in the pH range 4.0-6.5 yielding 2 distinct homogeneous peptides, alpha and beta, capable of suppressing hCG-induced uterine weight increase in immature mice, in a 'reversed Steelman-Pohley' assay design. However, of these, alpha alone was able to suppress post-castrational serum gonadotropin rise in appropriate animal models. This peptide is highly acidic in nature (iso-electric point congruent to 2.2) and has a molecular weight (Mr) of 18200 and a Stokes radius of 1.90 nm. On the basis of currently available evidence, it is concluded that the molecule consists of a single peptide chain.

Isolation of porcine follicular fluid inhibin of 32K daltons

Purification of ovarian inhibin from porcine follicular fluid was performed by using an bioassay based upon the suppression of spontaneous FSH release from cultured cells of rat anterior pituitary. The presence in the follicular fluid of four molecular forms of inhibin activity corresponding to Mr 100K, 80K, 55K and 32K was revealed by SDS-gel electrophoresis under non-reducing conditions. The smallest inhibin amongst them, named 32K inhibin, eliciting about 70% of the total activity in the follicular fluid, was separated by gel filtration in the presence of 8 M urea. By subsequent ion-exchange chromatography, followed by RP-HPLC, 32K inhibin was purified to homogeneity with a 8,000 fold purification factor in a yield of 12%. The purified 32K inhibin was found to comprise two polypeptide subunits (Mr 20K and 13K), linked by disulfide bridges and to specifically suppress the secretion of FSH, but not of LH from the pituitary cells.

Human seminal alpha inhibins: isolation, characterization, and structure

Two additional peptides with inhibin-like activity have been isolated from human seminal plasma. One consists of 52 amino acids and the other, 92 amino acids. They are designated alpha-inhibin-52 and alpha-inhibin-92. Sequence analyses show that the NH2-terminal 31 amino acids of alpha-inhibin-52 are identical to the structure of the inhibin-like peptide previously reported [ILP-(1-31), now designated alpha-inhibin-31], and the COOH-terminal 52 amino acids of alpha-inhibin-92 are identical to the structure of alpha-inhibin-52. The amino acid sequence of alpha-inhibin-92 is: (sequence in text) Bioassay data in mouse pituitaries in vitro show that alpha-inhibin-52 is 3.4 times more active and alpha-inhibin-92 is greater than 40 times more active than alpha-inhibin-31 in suppressing follitropin-release. Radioimmunoassay data indicate that alpha-inhibin-52 and alpha-inhibin-92 have only 60% immunoreactivity.

Amino acid sequence of the predominant basic protein in human seminal plasma

The predominant basic protein in liquefied human seminal plasma is the major degradation product of the gel-forming protein secreted by the seminal vesicles. The amino acid sequence of this basic protein is presented. The basic protein contains 52 amino acid residues. It is devoid of cysteine, methionine, tryptophan, and leucine, but contains seven histidine residues located in the NH2-terminal half of the molecule. The calculated Mr of 5753 is in close agreement with that obtained from gel filtration in guanidine-HCl on Sephacryl S-200 (Mr = 6000).

beta 2-Inhibin contains the active core of human seminal plasma beta-inhibin: synthesis and bioactivity

The complete synthesis of the C-terminal 28 residues segment 67-94 of human seminal plasma beta-Inhibin, called beta 2-Inhibin, is reported. The Inhibin-like activity of the native 94 amino acids beta-Inhibin is compared to that of the synthetic replica of beta 2-Inhibin. In all assays used both peptides effectively suppress the FSH release induced by LHRH but have little effect on the LH release. In the mouse both peptides are equipotent on a mole basis. In the rat the synthetic beta 2-Inhibin is 3-10 times more potent than beta-Inhibin. Both peptides are active in rat anterior pituitary primary culture assays where maximum suppression of FSH release induced by LHRH occurs around 300 pmol/ml of beta 2-Inhibin. In contrast, maximum suppression of FSH release in the mouse pituitary assay occurs at 10-15 pmol/ml of either Inhibin.

Isolation of inhibin from bovine follicular fluid

Bovine follicular fluid was used as a source for the isolation of gonadal inhibin, the activity of which was monitored by the dose dependent suppression of the FSH content of cultured pituitary cells. The procedures presented result in over 3000-fold purification of the starting material and the purified inhibin has an apparent molecular weight of 56000. The purified inhibin can be dissociated under reducing conditions into two subunits with molecular weights of 44000 and 14000 daltons.

Evidence that synthetic 31-amino acid inhibin-like peptide lacks inhibin activity

We studied the biological activity of a recently characterized 31-amino acid inhibin-like peptide (ILP) using a synthetic preparation. While the material yielded a single component on chromatography, amino acid sequence analysis suggested that only 30% of the molecules possess the complete structure. Bioactivity was tested in vitro using whole pituitaries from 25 day-old male Sprague-Dawley rats. Pituitaries were incubated with 500 ng/ml of the ILP preparation or vehicle alone for 60 min, followed by a 3 h exposure to 2 ng/ml of luteinizing hormone releasing hormone (LHRH) or its diluent. In the ILP-incubated pituitary media, no significant suppression of basal FSH and LH release or stimulated FSH release was observed, while a significant increase in stimulated LH release was seen (p less than 0.05). An in vivo bioassay study was performed on 38 day-old male Sprague-Dawley rats. Test animals were injected with 0.1, 1, 10 or 20 mcg of ILP immediately after castration, and 10 and 24 h later. Control animals received bovine serum albumin or vehicle alone. There were no statistically significant differences in serum LH or FSH concentrations taken at 30 h after castration between the ILP-treated rats and controls. Possible reasons for our inability to demonstrate inhibin bioactivity (selective FSH suppression) with this ILP preparation include: Only about 30% of the peptides had the complete amino acid sequence. Other peptides with deletions might have acted as antagonists, thus obscuring the inhibin bioactivity. The 31-amino acid ILP may not be the authentic inhibin molecule. We suggest that further studies are needed to determine the true identity of inhibin.

Demonstration of a gradient in inhibin activity, estrogen, progesterone, and delta 4-androstenedione in follicular fluid, ovarian vein blood, and peripheral blood of normal women

Ovarian vein serum from 3 subjects during the late follicular phase of the menstrual cycle had detectable inhibin activity, whereas ovarian vein serum of 12 other subjects during the early follicular phase and luteal phase had no detectable inhibin activity in a rat anterior pituitary cell culture assay. Subjects having detectable inhibin activity (102 +/- 47 U/100 microliters) had 1257 +/- 582 U/100 microliters inhibin activity in FF, whereas subjects having no detectable inhibin activity had FF levels of 711 +/- 203 U/100 microliters of inhibin activity. Estrogen levels of FF and ovarian vein serum of the group having detectable inhibin activity in ovarian vein serum were 282 +/- 239 ng/ml and 4.8 +/- 1.77 ng/ml, respectively. The estrogen content of FF and ovarian vein blood of the group having nondetectable inhibin activity in ovarian vein blood was 127 +/0 45 ng/ml and 3.03 +/- 0.6 ng/ml, respectively.

Cellular immunolocalization of inhibin-like peptide in human benign prostatic hyperplasia

Immunoperoxidase staining method and specific antisera against highly purified inhibin-like material (ILM) from human seminal plasma were utilized to localize immunoreactive ILM in benign hyperplastic prostate (BPH) in human. Immunoreactive ILM was strictly localized to glands of hyperplastic nodules. The concentration of ILM was more in epithelial cells lining the healthy lobule than in those undergoing atrophy.

Use of fast protein liquid chromatography in the purification of inhibin from bovine follicular fluid

Inhibin from bovine follicular fluid was partly purified using affinity chromatography on immobilized Procion Red 3B, gel filtration on Sephadex G-25 and ion-exchange chromatography on the fast protein liquid chromatography system. Inhibin was subsequently characterized using preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis and electroelution. Biological activity was associated with a protein with an apparent molecular weight of approximately 65 kD.

Complete amino acid sequence of human seminal plasma beta-inhibin. Prediction of post Gln-Arg cleavage as a maturation site

The complete sequence of a 94 amino acid human seminal plasma polypeptide exhibiting inhibin-like activity is presented. This molecule, called beta-inhibin, selectively and specifically suppresses the release of pituitary FSH in vivo as well as in vitro. It does not affect the secretion of LH. Such a novel acidic protein contains a very basic C-terminal segment which is easily cleaved by mild tryptic digestion. It is predicted that the FSH inhibiting activity may reside within this region of the molecule. This would imply a post Gln-Arg cleavage to release the basic C-terminal active moiety.

Evidence for the prostatic origin of immunoreactive inhibin-like material in human seminal plasma

Inhibin is defined as a gonadal peptide exerting an inhibitory effect on the secretion of follicle-stimulating hormone (FSH) by the pituitary. Using a radioimmunoassay (RIA) procedure developed for a homogeneous inhibin-like peptide with a molecular weight of 14 000 daltons isolated from human seminal plasma, immunoreactive inhibin-like matrial (ILM) was quantitated in serum, urine and semen of men in order to investigate its origin. Vasectomy did not result in a significant reduction in seminal plasma ILM. Determination of ILM immunoreactivity in ejaculates form normal men and semen samples characterized by prostate-rich and prostate-deficient secretions, indicated high levels of ILM in the prostatic secretions. Immunoreactive ILM levels estimated in different fractions of split ejaculates from normal men paralleled those of zinc and acid phosphatase activity and were significantly higher in fractions representing prostatic secretions compared to those representing the secretions of seminal vesicles. Estimation of ILM in semen, serum and urine from bilaterally gonadectomized men showed that immunoreactive ILM levels remained high after gonadectomy. It is concluded that the bulk of the immunoreactive ILM present in the semen, blood and urine of men is not secreted by the testes. The principal site of origin of this material, at least in semen, appears to be the prostate.

Synthesis and biological activity of human inhibin-like peptide-(1-31)

A peptide containing 31 amino acids with inhibin-like activity has been synthesized by the solid-phase method. The synthetic product was shown to be homogeneous in high-performance liquid chromatography and paper electrophoresis. In the mouse pituitary incubation system, the follitropin-suppressing activity of the synthetic peptide was comparable to that of the natural product. It was also active in suppressing lutropin-releasing hormone-induced follitropin release in vivo in immature male rats.

Porcine inhibin: initial fractionation as a high molecular weight complex

A high molecular weight complex or aggregate of inhibition was obtained by chromatography of porcine follicular fluid in Fractogel TSK65F. Recovery of activity was good (usually 80-100%), but only 30-60% was recovered as a high molecular weight complex (greater than 160,000) free of albumin and gamma globulin (the two major proteins in follicular fluid). The balance of the activity was distributed in the gamma globulin-albumin region of the chromatogram (i.e., 160,000 down to 65,000 daltons). Distribution in this region of the chromatogram in part reflected the prior processing of the sample (e.g., it was augmented by ethanol or acetone precipitation prior to chromatography). The utility of Fractogel chromatography lies in its ability to resolve a large portion of the inhibin activity from the major proteins (albumin and gamma globulin), plus an efficient recovery of activity. Maximum purification on the Fractogel chromatograms was approximately 20-fold. This product and the other Fractogel fractions were tested for protease activity by a sensitive slab gel procedure. All fractions contained detectable protease activity that could potentially affect inhibin activity during further fractionations. This was shown with a protease fraction isolated from porcine follicular fluid by affinity chromatography. When added to a partially purified inhibin preparation, this protease fraction destroyed 77% of the inhibin activity.