Isolation and characterization of alpha-N-acetyl beta-endorphin(1-26) from the rat posterior/intermediate pituitary lobe

Revised primary structures of rat pituitary gamma-lipotrophin and beta-endorphin

In-depth investigations, by high performance liquid chromatographic purification, radio-immunoassay, mass spectrometry, tandem mass spectrometry, Edman sequencing and limited C-terminal ladder sequencing, were prompted by mass spectrometric charting experiments which suggested that the amino acid sequences for rat gamma-lipotrophin and beta-endorphin require revision. The results for gamma-lipotrophin identify a histidine for glutamine substitution at position 12, and heterogeneity in the expressed protein presumably due to partial dehydration. Partial dehydration for acidic joining peptide, previously reported by Toney et al was corroborated. The results for beta-endorphin confirm the presence of alanine at position 26 and provide no evidence for the expression of multiple forms of the hormone.

Forms of immunoreactive beta-endorphin in the intermediate pituitary of the holostean fish, Amia calva

Acid extracts of the intermediate pituitary of the holostean fish, Amia calva, were fractionated by gel filtration chromatography and analyzed with radioimmunoassays specific for N-acetylated beta-endorphin and C-terminally amidated alpha-MSH. In these extracts beta-endorphin-related immunoreactive material and alpha-MSH-related immunoreactive material were present in roughly equimolar amounts. The immunoreactive beta-endorphin-sized material was tested for opiate receptor binding activity using a beta-endorphin radioreceptor assay. The results of these studies were negative. The immunoreactive beta-endorphin-sized material was further analyzed by cation exchange chromatography at pH 2.5. Two major and three minor peaks of immunoreactive material were isolated. Peak 5 exhibited a net charge of +7 at pH 2.5 and represented 53% of the total immunoreactivity recovered. Peak 2 with a net charge of +3 at this pH represented 38% of the total immunoreactivity recovered. The minor forms, Peaks 1, 3 and 4, exhibited net charges of +2, +4 and +6, respectively. The apparent molecular weights of Peaks 2 and 5 were determined on a Sephadex G-50 column. Peak 2 had an apparent molecular weight of 2.7 Kd and Peak 5 had an apparent molecular weight of 3.5 Kd. Reverse phase HPLC analysis of Peak 5 indicates that this form of Amia beta-endorphin had chromatographic properties similar to salmon beta-endorphin II. These results would suggest that N-terminal acetylation and C-terminal proteolytic cleavage are important post-translational modifications of the forms of Amia beta-endorphin.

N-acetylated endorphins in ovine anterior pituitary and neuro-intermediate lobe

We have used an antiserum for immunohistochemistry and RIA/RP-HPLC which recognizes all fragments of N-acetylated endorphin (NacEP). In the rat neuro-intermediate lobe (N-IL), in addition to the N-acetylated forms of immunoreactive-beta-endorphin (ir-beta EP) already reported, we have demonstrated Nac beta EP as a minor component. In the sheep pituitary processing of beta EP is markedly different. In the anterior pituitary (AP), staining was indistinguishable with beta EP and NacEP antisera, in contrast with the rat where many fewer AP cells stained with the NacEP antiserum. Secondly, as in the rat, all N-IL cells stained with both antisera; on RP-HPLC, however, the major forms of NacEP in the sheep N-IL were Nac beta EP (approximately 40%), Nac beta EP (approximately 25%) and Nac beta EP (approximately 20%), with Nac beta EP (approximately 2%) as a minor component. A similar profile was seen on RP-HPLC of sheep AP. These data suggest that (1) patterns of processing in sheep AP are similar to those in N-IL, though the extent of acetylation is less and (2) in the sheep pituitary low molecular weight acetylated fragments predominate, in contrast with the rat.

Isolation of immunoreactive beta-endorphin-related and Met-enkephalin-related peptides from the posterior pituitary of the amphibian, Xenopus laevis

Acid extracts of the posterior pituitary of the amphibian, Xenopus laevis, were analyzed with two heterologous region specific beta-endorphin RIAs. Following gel filtration chromatography and cation exchange chromatography four peaks of immunoreactivity were detected. All four peaks were detected with a N-acetyl specific beta-endorphin RIA. Peak I represented 92% of the total immunoreactivity isolated following cation exchange chromatography. This peak had a net positive charge at pH 2.5 of +1 and an apparent molecular weight of 1.4 Kd. Following reverse phase HPLC, Peak I fractionated into two peaks: Peak Ia and Peak Ib. Both peaks were detected with the N-acetyl specific beta-endorphin RIA and a Met-enkephalin RIA, however, neither peak co-migrated with either Met-enkephalin or N-acetyl-beta-endorphin(1-16). At present it is not clear whether Peak I is derived from pro-opiomelanocortin or one of the other opioid polyproteins. Peaks II, III, and IV represented 8% of the total immunoreactivity recovered following cation exchange chromatography. These peaks had net positive charges of +3, +4, and +5, respectively, and apparent molecular weights of 2.8, 3.2, and 3.5 Kd, respectively. These apparently N-acetylated beta-endorphin-sized forms are minor end products of the pro-opiomelanocortin biosynthetic pathway.

Characterization of immunoreactive beta-endorphin secreted from cultured human corticotropin-secreting adenomas

Seven human corticotropin-secreting adenomas causing Cushing's disease or Nelson's syndrome were maintained in long-term culture. Pooled media from the individual adenomas were analyzed for the composition of their secretory products. From a radioimmunoassay (RIA) with 100% cross-reactivity for human beta-endorphin (beta h-EP) and beta-lipotropin (beta h-LPH), immunoreactive beta h-EP (IR X beta h-EP) was found to be the predominant secretory product after Sephadex G-50 analysis in 4 cases (40-80% of total IR), immunoreactive beta h-LPH (IR X beta h-LPH) predominated in 1 case, and both were equipresent in 2-cases. IR X beta h-EP was further purified by high-performance liquid chromatography (HPLC) and analyzed in 4 cases with ion-exchange chromatography on SP-Sephadex C-25 and a RIA which completely cross-reacts with beta h-EP, [N alpha-Ac]-beta h-EP, beta h-EP-(1-27) and [N alpha-Ac]-beta h-EP-(1-27). In all cases, the IR X beta h-EP was the main component (40-70%); the remaining IR material was attributable partially to [N alpha-Ac]-beta h-EP or other, less defined immunoreactive material. In 3 cases, enough IR X beta h-EP material was available for HPLC and to perform a radioreceptor assay using tritiated beta h-EP as primary ligand. The displacing potency of these preparations relative to synthetic beta h-EP was related to the content of the immunoreactive component eluting in the position of synthetic beta h-EP.

Localization of neurons containing pro-opiomelanocortin-related peptides in the hypothalamus and midbrain of the lizard, Anolis carolinensis: evidence for region-specific processing of beta-endorphin

Immunohistochemical analyses of the lizard-brain, following colchicine pretreatment, revealed two populations of POMC-producing cell bodies located in medial-basal hypothalamus and the mesencephalic tegmentum. Analyses of extracts of lizard brain regions by radioimmunoassay and gel filtration chromatography indicate that beta-endorphin-sized and alpha-MSH-sized peptides are the major POMC-related end products. Evidence is presented for region-specific processing of beta-endorphin in the lizard brain.

Chromatography of peptides related to beta-endorphin

Chromatographic procedures are described here for the resolution of beta-endorphin and its related peptides at picomolar concentration. Initially gel filtration is carried out on Sephadex G75 in 50% acetic acid, providing peptides with the approximate molecular size of beta-endorphin. The group of beta-endorphin-related peptides is resolved by ion-exchange chromatography on the pyridinium form of sulfopropyl Sephadex C25 in the presence of 50% acetic acid. The addition of 125I-labeled marker peptides prior to chromatography allows the recovery of each peptide to be calculated and provides a guide for identifying the elution positions of the endogenous peptides. Additional resolution can be obtained by high-pressure liquid chromatography (HPLC) of the sulfoxide forms of the peptides on muBondapak C18 under acidic conditions. The advantages and disadvantages of ion-exchange chromatography and high-pressure liquid chromatography are discussed for the purification of small amounts of basic, hydrophobic peptides.

Further characterization of the major forms of reptile beta-endorphin

Biosynthetically labeled reptile intermediate pituitary beta-endorphin-sized material was fractionated by SP-Sephadex ion exchange chromatography into two major opiate-active forms which eluted at 0.28 M NaCl and 0.32 M NaCl, respectively; the 0.32 M form of reptile beta-endorphin (mw = 3500), serves as the precursor for the 0.28 M form of reptile beta-endorphin (mw = 3200), (Dores and Surprenant, 1983). Analysis of tryptic digests of these reptile beta-endorphins by paper electrophoresis at pH 3.5 and gel filtration on a Sephadex G-15 column indicated that there are two tyrosine residues, two arginine residues and one methionine residue in reptile beta-endorphin. Furthermore, the NH2-terminal tryptic peptide of both reptile beta-endorphins is approximately nine amino acids in size and contains tyrosine, methionine and arginine. Analyses of chymotryptic/protease digests of the [3H]tyrosine-labeled NH2-terminal tryptic peptide analyzed by descending paper chromatography revealed that the NH2-terminal tyrosine of reptile beta-endorphin is not alpha-N-acetylated. A second tyrosine-containing tryptic peptide was detected in the COOH-terminal region of reptile beta-endorphin; however this tryptic peptide differs in the two forms of reptile beta-endorphin in terms of size and net charge at pH 3.5. These differences account for the apparent molecular weight differences and distinct ion exchange properties of the 0.28 M and 0.32 M forms of reptile beta-endorphin. Thus in the reptile intermediate pituitary the principal post-translational mechanism for modifying beta-endorphin is COOH-terminal proteolytic cleavage.

Biosynthesis of multiple forms of beta-endorphin in the reptile intermediate pituitary

Fractionation of the beta-endorphin-sized material from freshly dissected reptile intermediate pituitaries by ion exchange chromatography on sulfopropyl Sephadex (SP) revealed at least three distinct forms of immunoreactive beta-endorphin. These forms eluted at 0.25 M NaCl, 0.28 M NaCl, and 0.32 M NaCl and represent respectively, 6%, 65% and 29% of the total immunoreactivity. Only the 0.28 M NaCl peak and the 0.32 M NaCl peak exhibited naloxone reversible opiate bioactivity when tested in the isolated guinea pig ileum bioassay system; taking into account the molar amount of immunoreactive peptides the 0.32 M NaCl peak was 6 fold more potent than the 0.28 M NaCl peak. Intermediate pituitaries in culture were incubated with either [3H]tyrosine, [3H]arginine, or [35S]methionine for periods up to 24 hours and beta-endorphin-sized peptides were prepared by immunoprecipitation and gel filtration. Fractionation of the labeled beta-endorphin-sized peptides by ion exchange chromatography yielded profiles nearly identical to the immunoassay analyses of freshly dissected tissue. Further analysis of the major labeled forms of reptile beta-endorphin by chromatography on Sephadex G-50 equilibrated in 6 M guanidine HCl indicated that the 0.32 M NaCl peak had an apparent molecular weight of 3500 +/- 100 and the 0.28 M NaCl peak had an apparent molecular weight of 3200 +/- 100. Furthermore, pulse/chase experiments showed that the 0.32 M NaCl peak was the precursor for the 0.28 M NaCl peak. These results coupled with the relative opiate bioactivities of the major argue that the principal post-translational modification of reptile beta-endorphin is COOH-terminal proteolytic cleavage.

Measurement of total opioid peptides in rat brain and pituitary by radioimmunoassay directed at the alpha-N-acetyl derivative

A sensitive assay, which cross-reacts with and is specific for diverse opioid peptides, is described. This is based on the prior acetylation of samples and subsequent radioimmunoassay with an antiserum highly specific for the acetylated NH2 terminus of opioid peptides. The result is a procedure that can be used to investigate multiple forms of opioid peptides in extracts of biological material. The sensitivity of the assay is approximately 15 fmol of beta-endorphin per incubation tube, i.e., approximately 100-fold greater sensitivity than the radioreceptor assay used in our laboratory. The peptide concentration required for 50% displacement of trace ranged from 0.65 nM (beta-endorphin) to 1.6 nM (Met-enkephalin). The assay apparently shows an absolute requirement for a free (or acetylated) NH2 terminus corresponding to either a Leu- or Met-enkephalin sequence. Use of the assay with and without prior acetylation of sample provides a method for estimation of the ratio of acetylated:nonacetylated opioid peptides in crude or fractionated extracts. The procedure is used to investigate the forms of opioid peptide found in rat brain and pituitary.

alpha-N-acetyl-beta-endorphin1-26 from the neurointermediary lobe of the rat pituitary: isolation, purification, and characterization by high-performance liquid chromatography

The neurointermediary lobes from 190 rat pituitaries were homogenized in an acidic medium which inhibits peptidase activity and maximizes the solubilization of undamaged peptides. Octadecylsilyl-silica (ODS-silica) was used to extract the supernatant of the tissue homogenate. The ODS-silica eluate, now largely protein and salt free, was subjected to reversed-phase high-performance liquid chromatography (HPLC) employing 0.1% trifluoroacetic as counter ion. The column eluates were monitored for beta-endorphin immunoreactivity. Five immunoreactive components were observed. The most hydrophobic of these was repurified on the same HPLC column using 0.13% heptafluorobutyric acid as counter ion. Characterization of the purified peptide by gel permeation HPLC, amino acid analysis, and tryptic fragmentation indicated that it corresponded in structure to alpha-N-acetyl-beta-endorphin1-26. Amino acid analysis of the native peptide and its trypsin and carboxypeptidase fragments indicated that an alanyl residue occupies position 26. This finding is in contrast to the sequence predicted for the beta-lipotropin/corticotropin precursor by recombinant DNA techniques which suggests that the 26th residue of the beta-endorphin molecule should be valine.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.

Opioid peptides as neuroregulators: potential areas for the study of genetic-behavioral mechanisms

The opioid peptides have been related to behavior in both animal and human studies. Further investigation can be anticipated which could lead to the elucidation of genetic controls over enzymes which process these peptides and the receptors upon which the peptides act. The enzymes, both synthetic and degradative, can lead to the formation of different forms of the opiate peptides. Differential control of these enzymes or of the multiple forms of opiate receptors could lead to discrete changes in opiate status and subsequent behavioral changes. Conversely, genetically regulated behavioral modification could also lead secondarily to opiate changes.