Hypothalamic processing of beta-endorphin in female C57BL/6J mice is altered at middle age

beta-Endorphin (beta-endo) (1-31) is the active opioid peptide product of pro-opiomelanocortin processing. Further post-translational modifications of beta-endo(1-31) yield beta-endo(1-27), (1-26) and their acetylated forms which are considered to be opiate receptor antagonists. Mechanistically, alteration in opiatergic properties is likely to result in the loss of a number of physiological functions including reproductive capacity. The purpose of this study was to determine whether there are changes in the way beta-endo neurones process the peptide with age in female C57BL/6J mice. Pooled extracts of arcuate nucleus (ARC) and preoptic area (POA) of 3- to 4-month-old normally cycling (4-5 days at dioestrus), 12- to 13-month-old irregularly cycling (5-7 days at dioestrus), 23- to 24-month-old acyclic (in persistent dioestrus) animals were subjected to reversed-phase HPLC (n = 4 experiments). Column fractions were assayed for beta-endo-like-immunoreactivity by sequence-specific RIAs. The opiate receptor active as well as opiate receptor antagonist forms of beta-endo were present in both ARC and POA at all three age groups although their ratios varied. beta-Endo(1-31), the active opiate, was the predominant form in young animals. At middle age there was a threefold (P < 0.05, ANOVA) increase in the antagonist forms of beta-endo and this was associated with a significant (P < 0.05, ANOVA) increase in the ratio of antagonist to active forms. This was accompanied by a trend toward an increase in acetylated forms of beta-endo in middle-aged mice. HPLC profiles from hypothalami of old animals more closely resembled those of young females. The increase in the antagonist forms of beta-endo at middle age may contribute to a decline of opiatergic influences in the female C57BL/6J mouse and suggest a mechanism whereby alterations in opiate influence over gonadotrophin control may occur.

Immunocytochemical localization of granulin-1 to mononuclear phagocytic cells of the teleost fish Cyprinus carpio and Carassius auratus

A new class of low-molecular-weight cysteine-rich regulatory growth factors, designated granulins, has been isolated from hematopoietic tissues of a teleost fish (Cyprinus carpio) and structurally characterized. Granulin-1, the predominant form found in carp spleen, was used to raise polyclonal antibodies in rabbits and to establish a radioimmunoassay. This permitted preliminary tissue distribution studies of granulin-1 to be undertaken in carp (Cyprinus carpio) and goldfish (Carassius auratus). Granulin-1 immunoreactivity was found in the melanomacrophage centers of the spleen and head kidney. Carp tissues anatomically involved in the first line of defense against infection, including skin, gills, gut, and also heart, showed intense granulin-1 immunoreactive staining within presumptive macrophage cells. Granulin-1 immunoreactive macrophages prepared from goldfish spleen and head kidney adhered to glass slides, actively phagocytosed carbon particles, and contained granulin-1 immunoreactivity as well as abundant endogenous peroxidase activity. This study demonstrates that granulin-1 is synthesized and stored in macrophages/monocytes of spleen, head kidney, and peripheral tissues of teleost fish.

Purification of antimicrobial peptides from an extract of the skin of Xenopus laevis using heparin-affinity HPLC: characterization by ion-spray mass spectrometry

A simple scheme was developed for the rapid purification of antimicrobial peptides from the skin of Xenopus laevis. An extract of the frog skin was prepared using an acidic medium designed to maximize the solubilization of low-molecular-weight peptides. This extract was subjected to an enrichment procedure using C18 Sep Pak cartridges to yield a salt-free fraction, devoid of high-molecular-weight proteins. This fraction was in turn subjected to heparin affinity high-performance liquid chromatography on a Shodex AF-Pak column. All the antibacterial activity bound to the column and could be eluted using a linear gradient of increasing sodium chloride concentration. Antibacterial activity emerged from the column in fractions corresponding to a sodium chloride concentration of 0.45 M. Reversed-phase high-performance liquid chromatography resolved this material into a series of compounds which could be readily characterized using a combination of amino acid analysis and ion-spray mass spectrometry. Each peptide was found to be antimicrobial and each was positively identified as belonging to a family of amphipathic helix-forming peptides characterized by other investigators. Listed in their order of elution from the reversed-phase column the peptides were magainin 2, magainin 1, peptide-glycine-leucine amide, xenopsin precursor fragment, levitide precursor fragment, and a mixture of fragments derived from the caerulein precursor. These peptides owe their antimicrobial properties to a predeliction to forming amphipathic alpha-helical structures when associated with lipid membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

O-glycosylation mimics N-glycosylation in the 16-kDa fragment of bovine pro-opiomelanocortin. The major O-glycan attached to Thr-45 carries SO4-4GalNAc beta 1-4GlcNAc beta 1-, which is the archetypal non-reducing epitope in the N-glycans of pituitary glycohormones

The NH2-terminal domain of pro-opiomelanocortin, designated as the 16-kDa fragment, is highly conserved throughout the vertebrate family and is likely therefore to have an important functional role. Bovine 16-kDa fragment is a 77- residue glycopeptide, which has been found to be glycosylated at threonine 45 and asparagine 65. Available evidence suggests that glycoforms lacking glycans at the O-linked site are processed in the intermediate pituitary at -Arg49-Lys50- to give the residue 1-49 amino-terminal peptide and a carboxyl-terminal glycopeptide referred to as Lys1 gamma 3-melanotropin. Glycoforms carrying O-glycans remain unprocessed in the intermediate pituitary. Thus O-glycosylation is likely to play an important role in controlling the fate of the NH2-terminal portion of pro-opiomelanocortin, thereby affecting the biological events that are influenced by peptides and glycopeptides derived from this domain. In a recent study (Siciliano, R. A., Morris, H. R., McDowell, R. A., Azadi, P., Rogers, M. E., Bennett, H. P. J., and Dell, A. (1993) Glycobiology 3, 225-239), we sequenced the N-glycans attached to Asn-65 of bovine 16-kDa fragment and demonstrated that the acidic components contain, in addition to neutral antennae, a single SO4-4GalNAc beta 1-4GlcNAc beta 1- antenna, which is characteristic of the pituitary glycohormone N-glycans (Baenziger, J. U., and Green, E. D. (1988) Biochim. Biophys. Acta 947, 287-306). We now report the structural characterization of the O-linked oligosaccharides found in bovine 16-kDa fragment. The major component, which constitutes about 80% of the O-glycan population, is a novel sulfated tetrasaccharide, which carries the same sulfated epitope as the N-glycans. This is the first time that the SO4-4GalNAc beta 1-4GlcNAc beta 1- moiety has been observed in O-glycans, and it raises the interesting possibility that the beta-N-acetylgalactosaminyltransferase responsible for the addition of N-acetylgalactosamine to the pituitary glycohormones (Smith, P. L., and Baenziger, J. U. (1988) Science, 242, 930-933) might be capable of glycosylating both N- and O-linked acceptors.

Isolation and characterization of a cytostatic histone H2B-like protein from fetal lungs of non-diabetic and diabetic rats

It was observed in the course of other studies that rat fetal lung extracts inhibited proliferation of fetal lung cells in culture. The purpose of the present study was to isolate and characterize this cytostatic factor. It was found that fetal lungs contained a 16 kDa cytostatic factor and its concentration was twofold greater in fetal lungs of diabetic rats compared with control rats. This fetal lung cytostatic protein (FLCP) was purified by reversed-phase, heparin-affinity and gel filtration high-performance liquid chromatography and SDS-PAGE. The purified protein was electroblotted onto polyvinylidene difluoride membrane and subjected to sequence analysis. The amino-terminal sequence of this fetal lung cytostatic protein was P E P A K S A P A P X K G I G K Q X X K A X X K A ... and showed significant homology with histone H2B; however, the amino acid composition of FLCP suggested that it may be structurally distinct from histone H2B. Ion-spray mass spectrometry suggested that FLCP was made up of at least two species of the protein with molecular weights of 13,776.1 and 14,007.3 and was different from the molecular weight of rat histone H2B predicted by its cDNA sequence. The concentration of FLCP, based on amino acid compositions, was 0.32 nmol/g and 0.83 nmol/g wet fetal lung from non-diabetic and diabetic rats respectively. These findings suggest that the fetal rat lung produces a regulatory factor bearing considerable homology with but possibly different from histone H2B and that fetal lung immaturity during diabetic pregnancy might be contributed to by an increase in this factor.

The Lewis x epitope is a major non-reducing structure in the sulphated N-glycans attached to Asn-65 of bovine pro-opiomelanocortin

The N-terminal glycopeptide of pro-opiomelanocortin (POMC), designated as the 16K fragment, is highly conserved throughout vertebrates from amphibians to mammals and is likely therefore to have an important functional role. In this paper, we report the first structural characterization of N-glycans attached to asparagine-65 of a 16K glycopeptide. The 16K fragment was isolated from bovine pituitaries and the N-glycans were analysed using fast atom bombardment mass spectrometry together with sugar and linkage analysis. Sulphated-N-acetylgalactosamine-capped antennae, typical of the pituitary glycohormones, were present in the major acidic components. The POMC oligosaccharides are distinct from those of the pituitary glycohormones because the sulphate is exclusively located on the 3-arm of biantennary structures and, in addition, a significant proportion of the molecules carry the Lewis x epitope. It is probable that these differences reflect the absence of a tripeptide motif in POMC which fully conforms to the criteria previously defined for the recognition sequence for the N-acetylgalactosamine transferase that is specific for the pituitary glycohormones [Smith and Baenziger (1992) Proc. Natl. Acad. Sci. USA, 89, 329-333]. It remains to be seen whether the Lewis x epitope is involved in selectin-mediated events, but previous studies suggest that the sulphated moieties are unlikely to play a major role in clearance. The Lewis x epitope is also present in the neutral N-linked oligosaccharides, together with a variety of other antennae including a rarely found fucosylated GalNAc-GlcNAc structure.

Isolation and primary structure of the three major forms of granulin-like peptides from hematopoietic tissues of a teleost fish (Cyprinus carpio)

Granulins are cysteine-rich polypeptides purified from human and rat hematopoietic cells and structurally related to the epithelin family of growth modulatory factors. A prototypic form of granulin was isolated from the hematopoietic organs of teleost fish (Belcourt, D., and Bennett, H.P.J. (1988) J. Cell Biol. 107, 629 (abstr.)). This study reports the structure of three granulins purified from the spleen and head kidney of the carp (Cyprinus carpio). Ion-spray mass spectrometric analysis of granulin-1, -2, and -3 corroborated the observed primary structures and demonstrated that each 57-residue-peptide was monomeric in nature with all cysteines linked via intramolecular disulfide bridges. A comparison of the carp granulin sequences demonstrates that granulins 2 and 3 are most closely related with sequence variations occurring primarily toward the amino terminus. A rabbit polyclonal antibody was raised against carp granulin-1 to develop a radioimmunoassay for this peptide, which showed no significant cross-reactivity with granulin-2 and -3. The distribution of carp granulin-1 was studied by screening purified tissue extracts for immunoreactivity using reversed-phase high performance liquid chromatography. A single form of immunoreactive granulin-1 was identified in all carp tissues studied including spleen, head kidney, heart, skin, gills, and gut. These studies have established that members of the granulin/epithelin family are found in a lower vertebrate and may serve important growth modulatory functions throughout the vertebrate kingdom.

Aspartimide formation in the joining peptide sequence of porcine and mouse pro-opiomelanocortin

The joining peptide (JP) portion of pro-opiomelanocortin extracted from mouse pituitary glands has previously been shown to exist in one major and several distinct minor forms (Bennett, H. P. J. (1986) Peptides 7, 614-622). We now confirm the heterogeneous nature of JP extracted from mouse neurointermediate pituitary glands and show that similar forms of JP are also to be found in extracts of porcine pituitary glands. Three forms of porcine JP (pJP-A, pJP-B, and pJP-C) were purified from whole porcine pituitary glands using reversed-phase high performance liquid chromatography methods. The three structural variants constitute approximately 10, 75, and 15%, respectively, of the total JP observed. Mass spectrometric analysis revealed that pJP-C was 18 mass units smaller than pJP-B, which is consistent with the formation of a succinimide structure at the aspartyl 16-glycine 17 peptide bond. Such symmetrical imide structures are known to hydrolyze at physiological pH to yield a mixture of the original alpha-aspartyl peptides and isomerized isoaspartyl peptides. We were able to show that pJP-A was the isomerized isoaspartyl form by demonstrating that pJP-A but not pJP-B was a substrate for the protein carboxyl methyltransferase enzyme (L-isoaspartyl/D-aspartyl protein methyltransferase; EC 2.1.1.77) purified from bovine erythrocytes. This cytosolic enzyme is known to preferentially methylate L-isoaspartyl residues within model substrates. Control experiments in which JP was incubated in the acidic medium used to extract the pituitary tissue showed that the isoforms of pJP are not artifacts of peptide purification. Furthermore, we have isolated the isoforms of pJP at levels which are 100 times greater than would be expected for a spontaneous reaction. We conclude that the formation of the aspartimide form of JP appears to be a facilitated process, possibly occurring as a result of conformation constraints dictated by the structure of pro-opiomelanocortin, or an as yet uncharacterized post-translational event.

Nucleotide and (derived) amino acid sequence of a novel peptide from a rat (hypercalcemic) Leydig cell tumor

The nucleotide sequence of a novel peptide from a rat Leydig cell hypercalcemic tumor H-500 was determined. This cDNA encodes a peptide of 93 amino acids and contains a heparin binding domain similar to histone 2-B. Northern blot analysis showed tissue specific expression of this peptide mRNA.

Purification of cationic cystine-rich peptides from rat bone marrow. Primary structures and biological activity of the rat corticostatin family of peptides

Seven cationic, cystine-rich peptides of 29 to 32 amino acid residues have been purified from extracts of rat bone marrow (R-1, R-1a, R-1b, R-2, R-3, R-4 and R-5). Structural analysis clearly indicated that all seven peptides belong to the corticostatin/defensin family of leukocyte-derived peptides known to participate in oxygen-independent killing of phagocytosed bacteria. For R-1 to R-5, six cysteine residues were found at characteristic and highly conserved positions. R-1a and R-1b were partially characterized and appear to be structural variants of R-1. Aside from the conserved cysteines, there is a remarkable degree of structural diversity evident within the sequences of those members of the corticostatin/defensin family characterized so far. The structures of the peptides that we have purified can be compared directly with the sequences obtained for rat defensins isolated from extracts of peritoneal neutrophils (Lehrer, Ganz and Selsted, Cell, 64 (1991) 229-230). Some discrepancies are apparent which can be explained in terms of proteolytic cleavage of several of these peptides at both amino- and carboxyl-termini. The corticostatins owe their bioactivity to their ability to compete with corticotropin for occupancy of the corticotropin receptor (Zhu, Hu, Mulay, Esch, Shimasaki and Solomon, Proc. Natl. Acad. Sci. USA, 85 (1988) 592-596). The potency of these peptides can be expressed in terms of their capacity to inhibit the steroidogenic response of isolated rat adrenocrotical cells half-maximally stimulated by corticotropin (i.e., at the ED50 concentration for corticotropin in this assay, namely 33 pM). In this assay, the rat peptides R-1, R-2 and R-3 were shown to be inactive. In contrast, the more cationic peptides R-4 and R-5 were found to inhibit steroidogenesis. R-4 was somewhat less active than rabbit corticostatin (IC50 25 nM) showing an IC50 value of 50 nM. R-5 appeared to be significantly less potent than R-4. The lower yield of R-5 precluded an accurate estimate of the corticostatic potency of this peptide. R-4 differs in structure from R-5 in having an arginine to serine substitution at position 7. It can be concluded that an arginine at this position accounts, at least in part, for the corticostatic activity of R-4.(ABSTRACT TRUNCATED AT 400 WORDS)

Reversed-phase liquid chromatographic purification and isolation of a radio-iodinated selective probe for mu opioid receptors in the brain

A Guard-PAK precolumn system was used for the reversed-phase liquid chromatography purification of a small, synthetic radiolabeled opioid peptide, FK 33-824 (D-Ala2, methyl-phe4, Met (O)ol5 enkephalin) (FK). This procedure involves trace enrichment of iodinated peptide onto the precolumn while iodination reagents are not retained. Radioactive contamination of high-performance liquid chromatography columns and injectors is thus avoided. Precolumn chromatography has sufficient resolving power to separate not only labeled from unlabeled peptide but also mono- from di-iodinated peptide. Purified 125I-labeled FK (estimated specific activity 85.9-153.7 Ci/mmol) showed high specific binding to mouse corpus striatum, neocortex, cingulate cortex, nucleus accumbens septi, diagonal band of Broca, nucleus medialis septi, area preopticus magnocellularis, and the nucleus of the caudate/putamen. Radioligand binding was inhibited by both antagonists (naloxone and naltrexone); and agonists D-Ala2, N-methyl-phe4, gly-ol5-enkephalin [DAGO]; FK; and beta-endorphin at all concentrations tested (1 x 10(-8) to 1 x 10(-4) M). Adrenocorticotropin hormone (ACTH) did not block ligand binding at any concentration tested. Distribution of mu opioid receptors was analyzed by light microscopic autoradiography. Sections incubated with 125I-labeled FK in the presence of agonists and antagonists demonstrated decreasing ligand binding with increasing doses of competitor. ACTH did not block ligand binding at any concentration tested. HPLC analyses of ligand which had been iodinated 1.5 half lives before the date of the experiment demonstrated a single peak similar to that of freshly iodinated ligand. Similar binding kinetics and autoradiographic labeling patterns were observed as compared to those obtained with freshly iodinated peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of corticostatic peptides from guinea pig bone marrow

Three corticostatic peptides (GP-CS1, GP-CS2 and GP-CS3) were purified from extracts of guinea pig bone marrow. Each was identified on the basis of their ability to inhibit the secretion of corticosterone by isolated rat adrenal cells stimulated by ACTH. GP-CS1 and GP-CS2 were found to be 31 residues in length, rich in arginine and to have six cysteines typical of the corticostatin/defensin family of peptides previously purified from phagocytic cells of the immune system. GP-CS1 was found to be identical to GP-CS2 except for having a leucine at position 21 instead of isoleucine. GP-CS3 was also found to be rich in arginine and cysteine but structurally distinct from the other peptides. A combination of endoprotease mapping, ion-spray mass spectrometry and gas-phase sequencing revealed that GP-CS3 was a novel homo-dimer consisting of two 13 amino acid residue subunits cross-linked through eight cysteines in an anti-parellel configuration.

Effect of calcium ions on the processing of pro-opiomelanocortin by bovine intermediate lobe pro-opiomelanocortin-converting enzyme

The effect of Ca2+ on the extent and pattern of processing of pro-opiomelanocortin and an N-terminal fragment by a purified pituitary secretory vesicle, soluble aspartic endoprotease, was studied. Ca2+ stimulated the first cleavage of pro-opiomelanocortin by pro-opiomelanocortin-converting enzyme to yield 21-23 kDa adrenocorticotropin and beta-lipotropin, but its effect was minimal. The production of adrenocorticotropin from the 21-23 kDa intermediate was stimulated approximately 2.3-fold in the presence of 10 mM Ca2+, and processing of beta-lipotropin to beta-endorphin was stimulated about 1.3-1.4-fold by 5-10 mM Ca2+. The production of gamma-melanotropin-immunoreactive material from bovine N-pro-opiomelanocortin(1-77) was stimulated approximately 1.3-fold at both 100 microM and 1.5-2.0 mM Ca2+. Further characterization of the gamma-melanotropin-immunoreactive material by HPLC demonstrated that the major products were gamma 3-[Lys]melanotropin and gamma 3-melanotropin at both Ca2+ concentrations. These results indicate that pro-opiomelanocortin-converting enzyme is stimulated by Ca2+.

Differential glycosylation of N-POMC1-77 regulates the production of gamma 3-MSH by purified pro-opiomelanocortin converting enzyme. A possible mechanism for tissue-specific processing

The amino terminus of bovine pro-opiomelanocortin (N-POMC1-77) is partially processed in the intermediate lobe of the pituitary to N-POMC1-49 and lys-gamma 3-melanotropin. Two pools of N-POMC1-77 were isolated which were differentially glycosylated at threonine45, while N-POMC1-49 isolated from bovine intermediate lobe extracts existed in a non-glycosylated form. This suggested that differential O-linked glycosylation of N-POMC1-77 may regulate cleavage at the Arg49-Lys50 processing site. We tested this hypothesis by incubating N-POMC1-77 glycoforms with purified proopiomelanocortin converting enzyme. Only non-O-glycosylated N-POMC1-77 and O-glycosylated N-POMC1-77 with truncated oligosaccharide sidechains were sensitive to cleavage and generated predominantly lys-gamma 3-melanotropin, identified by high-performance liquid chromatography. These data provide the first functional evidence to support a role for differential O-linked glycosylation in the regulation of the processing of the N-terminus of bovine POMC.

Isolation and characterization of three forms of joining peptide from adult human pituitaries: lack of adrenal androgen-stimulating activity

Three structural variants of the joining peptide (JP) fragment of POMC have been purified from human pituitaries. Ion exchange and reverse phase tissue extraction procedures were combined with reverse phase HPLC to achieve complete purification of each form of JP. Fragments resulting from tryptic hydrolysis of each form were characterized by amino acid analysis and fast atom bombardment mass spectrometry. The predominant form of human JP, accounting for about 50% of the total purified, was found to be conjugated to glutathione through the lone cysteine residue at position 9. The other two variants were identified as human JP with a free cysteine residue and human JP dimer and accounted for 35% and 15%, respectively, of the total purified. Recently, human JP-(1-18) has been suggested as having adrenal androgen-stimulating activity. None of the three JP variants or their respective 1-20 amino-terminal fragments resulting from tryptic hydrolysis showed any ability to promote the secretion of dehydroepiandrosterone sulfate by cultured human fetal adrenal cells. Similarly, no potentiation of the stimulatory effects of ACTH-(1-39) was observed. The three variants of human JP as well as JP purified from rat, porcine, and bovine pituitaries were tested for their ability to stimulate androgenic steroids from dispersed fetal rabbit adrenal cells. None showed any significant biological activity either in stimulating steroid secretion or in potentiating the action of ACTH-(1-39).

Corticostatic peptides cause nifedipine-sensitive volume reduction in jejunal villus enterocytes

We studied cell-volume changes caused by adding corticostatin (CS) or defensin-like peptides to villus enterocytes isolated in suspension from guinea pig jejunum. Guinea pig CS (10(-9) M) added to villus cells in Na(+)-containing medium reduced volume, but immediate cell swelling was caused by 10(-6) M guinea pig CS. In Na(+)-free N-methyl-D-glucamine-containing medium 10(-9) M guinea pig CS accelerated the initial rate of shrinkage compared with cells in N-methyl-D-glucamine-containing medium alone as well as causing greater cell shrinkage. Guinea pig CS-stimulated cell shrinkage was prevented by a Ca2(+)-channel blocker--5 microM nifedipine, by chelation of extracellular Ca2+ with 100 microM EGTA, or by omega-conotoxin (10(-9) M). The Ca2+ ionophore A23187 (2.5 microM) reduced volume when added to villus cells in N-methyl-D-glucamine-containing medium; this action was prevented by EGTA, or quinine--an inhibitor of K+ conductance, or 9-anthracenecarboxylic acid--a Cl- channel blocker, suggesting that the volume reduction occurred because K+ and Cl- conductances were activated. Guinea pig CS-stimulated volume reduction was also prevented by 100 microM quinine or 9-anthracenecarboxylic acid. We conclude that jejunal villus enterocytes possess a Ca2(+)-activated Cl- conductance and a K+ conductance that need not be stretch-activated. Corticostatic peptides cause volume reduction in villus cells by activating L-type Ca2+ channels; other defensin-like peptides were without effect.

Production of monoclonal antibodies against the N-terminal glycopeptide of porcine pro-opiomelanocortin: their use for solid-phase radioimmunoassay, western blotting, and immunogold cytochemistry

We have prepared two monoclonal antibodies for the N-terminal glycopeptide of pro-opiomelanocortin 1-77 (N-POMC(1-77)) purified from porcine pituitaries. Antibody 1-244 recognizes an epitope located within the gamma 3-melanotropin (gamma 3-MSH or POMC(51-77)) sequence, whereas antibody 2-197 binds specifically to a determinant in the 1-49 region of N-POMC. These monoclonal antibodies were used to construct a two-site solid-phase radioimmunoassay that can detect as little as 50 pg of N-POMC(1-77). The assay is linear between 0.5 and 5 ng of porcine peptide and recognizes equally well the homologous peptides purified from human and bovine pituitaries. The assay has been used to analyze reversed-phase high pressure liquid chromatography fractions of crude bovine pituitary extracts and detected a peptide with chromatographic properties identical to those of N-POMC(1-77). When used to stain immunoblots of bovine intermediate pituitary extracts, both the 2-197 and 1-244 antibodies could recognize a major peptide comigrating with purified N-POMC(1-77). In addition, antibody 2-197 also detected a peptide with a mobility similar to that of standard N-POMC(1-49). When used in conjunction with a second anti-mouse antibody coupled to colloidal gold particles, antibody 2-197 stained N-POMC immunoreactive material located in granules in thin sections of pituitary.

Corticostatic peptides

In the last four years corticostatic (anti-ACTH) peptides have been isolated from human, rabbit, guinea pig and rat tissues. These peptides do not act via the cAMP cell signalling system but rather via the inhibition of the binding of ACTH to its receptor most probably through direct competition with the 14-18 sequence of ACTH for receptor binding. ACTH has specific high affinity receptors on adrenal cells but rabbit corticostatin I (CSI) has high capacity, low affinity receptors which are competed for by unlabelled excess CSI but not by excess ACTH. This indicates the presence of specific CSI adrenal cell receptors. The rabbit pituitary, hypothalamus, thalamus, adrenals, lungs and placenta contain sizeable amounts of immunoassayable CSI. Immunochemical localization of CSI indicates that it is present in the large macrophages and in neutrophils in rabbit lung, in macrophages and "supporting" endothelial cells in the spleen and in the adrenals in the cells of the zona reticularis. We have also isolated and identified new peptides which contain 12 cysteines from immune cells of humans, rats and a teleost, the carp. The functions of these peptides are now being determined. This large family of peptides may have many other, yet unidentified functions but at present we can only describe a small number of these.

Post-translational modification of bovine pro-opiomelanocortin. Tyrosine sulfation and pyroglutamate formation, a mass spectrometric study

The amino-terminal fragment of beta-lipotropin (i.e. beta-lipotropin (1-40)) and joining peptide portions of pro-opiomelanocortin have been purified from extracts of bovine posterior pituitaries. Peptides were purified using a combination of reversed-phase and ion-exchange batch extraction procedures followed by reversed-phase high performance liquid chromatography. beta-Lipotropin (1-40) was found to consist of four major components while joining peptide was found to consist of two major components. Fast atom bombardment-mass spectrometric analysis of the tryptic fragments of both peptides revealed that the observed heterogeneity could be explained in terms of post-translational modifications. beta-Lipotropin (1-40) was found to be sulfated at tyrosine residue 28 to an extent of about 50%. The tyrosine residue in beta-lipotropin (1-40) is situated within an amino acid sequence with a preponderance of glutamate residues. Sulfation of this amino acid residue is entirely compatible with the known primary structure requirements of the sulfotransferase enzyme located in the trans-Golgi fraction. Both beta-lipotropin (1-40) and joining peptide were found to have pyroglutamate at their amino termini to an extent of about 50%. The cDNA sequence for bovine pro-opiomelanocortin predicts the presence of glutamic acid at position 1 of both peptides. Pyroglutamate is normally formed through the cyclization of glutamine. This reaction is thought to be catalyzed by a pyroglutamate forming enzyme located within the secretory granule fraction. Under certain circumstances peptides with glutamate at their amino termini may act as substrates for this enzyme.

Purification of rat pro-atrial natriuretic factor: a simplified scheme using reversed-phase high-performance liquid chromatography

A simple scheme for the rapid and efficient isolation of rat pro-atrial natriuretic factor (pro-ANF) has been developed. An isolated rat adrenal cell bioassay for ANF was established to optimize heart tissue extraction and chromatography conditions. This assay is based on the ability of ANF to inhibit angiotensin II-stimulated aldosterone secretion. IC50 values for ANF were approximately 320 pM. The protocol that was established consisted of extraction of rat atria in 5 N acetic acid containing protease inhibitors. The extract was lyophilized, resolubilized in 0.1% trifluoroacetic acid containing 1% (w/v) sodium chloride, and subjected to RP-HPLC. Extraction of small batches of atria (i.e., from 10 or 20 rats) resulted generally in a yield of 2 nmol per rat (i.e., approximately 30 micrograms). The identity and purity of the pro-ANF were confirmed by the determination of both the amino acid composition and the amino-terminal sequence. Purified pro-ANF was radioiodinated and the efficiency of the extraction and purification procedure was assessed by adding labeled peptide to the initial tissue extract. The structural integrity and overall recovery of radioactivity were determined by RP-HPLC. The purification scheme provides undamaged pro-ANF of high purity. Purified pro-ANF was compared with synthetic rat ANF in the rat adrenal glomerulosa cell and isolated rat aortic strip bioassays. The peptides were apparently equally active in the adrenal cell system and approximately threefold less potent in relaxing aortic strips. The apparent equipotency in the adrenal cell bioassay may be due to the conversion of pro-ANF to ANF-like peptides during the bioassay incubation.

Processing of prosomatostatin

Several peptides are generated from prosomatostatin (proSS) in addition to somatostatin-14 (SS-14) and somatostatin-28 (SS-28). These are SS-28(1-12), proSS(1-76) and, as shown more recently, proSS(1-63) and antrin. Important variations in the proportion of these molecular forms are seen among different tissues and among different species. Processing of the precursor in the human brain yields minimal quantities of SS-28(1-12) and high levels of proSS(1-76), namely in cortical areas and in the bed nucleus of the stria terminalis. This is in contrast with findings in rat brain, where SS-28(1-12) is a predominant molecular form. Antrin, which corresponds to proSS(1-10), reaches its highest concentration in the antral portion of the stomach (117 +/- 13 pmol/g wet weight), where it is found in secretory granules of delta cells. We observed an inverse relationship between levels of antrin and proSS(1-63) after chromatography of various tissue extracts. This suggests a precursor-product relationship between these two peptides.

The amino acid sequence of chymodenin, a hormone-like peptide from porcine duodenum, is identical to cytochrome C-oxidase, peptide VII

The amino acid sequence of chymodenin, a hormone-like peptide from porcine duodenum is reported. The molecule is known to rapidly alter the proportions of digestive enzymes secreted by the rabbit pancreas in vivo and in vitro, by selection of the specific intra-pancreatic source from which the preset mixture of digestive enzymes is secreted. The sequence is identical to that of cytochrome C-oxidase peptide VII (cCoVII) from bovine heart, with the exception of a substitution of threonine for alanine at position 6 and a second substitution of alanine for threonine at position 71. Disulfide bridges link positions 29-64 and 39-53. cCoVII-chymodenin has a pentapeptide (-Ala-Glu-Gly-Thr-Phe-) near the carboxy-terminus which is immediately preceded by an -Arg-Arg- sequence in the porcine and bovine sequences of cCoVII. This peptide is identical to a pentapeptide found close to the amino terminus of the hormones gastric inhibitory peptide (GIP) and glucagon-like peptide I. The identity to cCoVII means chymodenin as isolated is itself unlikely to be a gastrointestinal hormone. However, the partial commonality of sequence with the glucagon-secretin family immediately adjacent to a pro-hormone-like activation site, and the specific actions on the exocrine pancreas, means that the molecule probably mimics the natural actions of an as-yet uncharacterized member of the glucagon family, which exerts a unique action on exocrine pancreatic secretion.

TRH stimulates the release of POMC-derived peptides from goldfish melanotropes

The release of immunoreactive (ir) alpha-MSH and ir ACTH from goldfish (Carassius auratus) melanotropes was investigated using superfused isolated dispersed neurointermediate lobe cell columns. Stimulation of neurointermediate lobe cell columns with pulses of TRH evoked dose-dependent increases in the concomitant release of ir alpha-MSH and ir ACTH. Reversed-phase high performance liquid chromatography (RP-HPLC) was used to characterize the alpha-MSH and ACTH immunoreactivities released from a neurointermediate cell column under spontaneous release conditions. Six peaks of ir alpha-MSH were revealed. Three of these peaks were identified as des-acetyl alpha-MSH, mono-acetyl alpha-MSH and di-acetyl alpha-MSH. Seven peaks of ir ACTH were revealed. Four of these peaks were tentatively identified as ACTH variants. These studies suggest that TRH stimulates the release of peptide hormones from teleost melanotropes and that the goldfish neurointermediate lobe in vitro releases numerous peptides derived from POMC.

A trace-enrichment technique for the loading of gel-permeation high-performance liquid chromatography columns

Gel-permeation high-performance liquid chromatography (GP-HPLC) columns provide rapid high-resolution separations but are frequently limited to analytical tasks because the injection volumes must be small. The reduction of volume required for the loading of solutes can often be impractical and lead to poor recoveries. We have developed a trace-enrichment technique to circumvent this problem. By placing a Waters Guard Pak within the loop of a Valco injector and connecting a pump to the injection port it is possible to concentrate proteins and peptides onto the guard column from relatively large volumes. Enrichment onto a reversed-phase guard column insert is achieved by loading solutes in an aqueous solution or one of low organic solvent concentration. Provided that the GP-HPLC is mean-while equilibrated with a solvent system of sufficiently high organic solvent concentration (i.e., 40% acetonitrile containing 0.1% trifluoroacetic acid) it is possible to elute material that has been loaded in this manner by simply placing the injection loop in line with the column. The solvent strength abruptly increases and the peptide or protein sample is loaded onto the column in a very small volume. We have applied this loading principle to both analytical and semipreparative problems. The amino-terminal fragment of pro-opiomelanocortin (POMC) has been extracted from a single human fetal pituitary (18 weeks gestation) and characterized in terms of its molecular weight. This study indicated that no proteolytic processing of the amino-terminal fragment of POMC takes place at this stage in development. In a larger scale application the amino-terminal fragment of POMC was purified from bovine anterior pituitaries.(ABSTRACT TRUNCATED AT 250 WORDS)