Isolation and primary structure of beta-endrophin and beta-lipotropin from bovine pituitary glands

Beta-endorphin-related peptides in the pituitary gland: isolation, identification and distribution

A new procedure is described for isolation of four forms of beta-endorphin from bovine pituitary. The four peptides are: the C-fragment of lipotropin (bovine lipotropin residues 63-93, or beta-endorphin, the alpha, N-acetyl derivative of the C-fragment, the C'-fragment (bovine lipotropin residues 63-89) and the alpha, N-acetyl derivative of the C'-fragment. Of these peptides, beta-endorphin alone possesses potent analgesic activity. The procedure has been applied in studying the distribution of beta-endorphin-related peptides in two regions of the pituitary. The results show that in the anterior pituitary of the pig and the rat, beta-endorphin is produced with a high degree of specificity in its opiate active form. In contrast, in the pars intermedia of both species at least six peptides related to beta-endorphin are elaborated and beta-endorphin represents only a minor component. The principal peptides in the pars intermedia have been identified as acetylated derivatives of lipotropin C'-fragment: in the pig the predominant peptide is alpha,N-acetyl C'-fragment and in the rat the major peptide appears to be an epsilon-acetylated derivative of alpha,N-acetyl C'-fragment. Thus, beta-endorphin is activated in the anterior pituitary and inactivated in the pars intermediate. The results demonstrate selective and specific processing of the 31K ACTH-endorphin prohormone in the different regions of the pituitary. In the anterior pituitary two biologically active peptides, ACTH and beta-endorphin, are generated together; in the pars intermedia alpha-melanotropin (alpha-MSH) is accompanied by forms of beta-endorphin that have been inactivated by acetylation and proteolysis.

The posttranslational modification of beta-endorphin in the intermediate pituitary of the toad, Bufo marinus, includes processing at a monobasic cleavage site

Fractionation of an acid extract of 15 B. marinus intermediate pituitaries by a combination of gel filtration chromatography and cation exchange chromatography revealed one major and five minor forms of beta-endorphin in this tissue. Based on reversed-phase HPLC and immunological properties, as well as amino acid composition and primary sequence analysis, it was deduced that the sequence of the major form of B. marinus beta-endorphin is N-acetyl-YGGFMTPE. Overall, the steady-state analyses of the minor forms of beta-endorphin indicated that the posttranslational processing of beta-endorphin in the toad intermediate pituitary includes endoproteolytic cleavage at both paired basic and monobasic cleavage sites.

Evidence for the presence of adrenocorticotropic and opiate-like hormones in the brains of two sea snakes, Hydrophis cyanocinctus and Lapemis hardwickii

The brain acetone powders of the sea snakes Hydrophis cyanocinctus and Lapemis hardwickii were extracted with a mixture of acetone:water:hydrochloric acid (40:21:1 by volume) and the extracts were then added to a copious volume of acetone, in accordance with the method of C. H. Li (1952, J. Amer. Chem. Soc., 74, 2134) for preparing adrenocorticotropin and beta-endorphin from mammalian pituitaries. The resultant precipitate, designated acid acetone powder, possessed adrenocorticotropic activity as evidenced in its ability to stimulate corticosterone production in isolated rat adrenal decapsular cells and lipolysis in isolated hamster adipocytes, and in its cross-reactivity in an ACTH radioimmunoassay. The presence of opioid molecules was indicated by activity in opiate radioreceptor assay using either 3H-D-Ala2-D-Leu5 enkephalin or [3H]naloxone as ligand and rat brain membranes. The brain acetone powders possessed neither "lactogenic" nor "somatogenic" activity as evidenced by their inability to displace the primary ligand in the rat hepatic prolactin receptor- and growth hormone receptor-binding assays, respectively.

Hormones with adrenocorticotropic and opiate-like activities from the carp (Cyprinus carpio) pituitary

Carp (Cyprinus carpio) pituitary acetone powder was extracted with a mixture of water, hydrochloric acid and acetone. An acid acetone powder was formed by adding the pituitary extract into a large volume of chilled acetone and subsequently recovering the precipitate. The powder was subjected to ion exchange chromatography on CM cellulose. Fractions adsorbed on the ion exchanger exhibited ACTH-like activity as evidenced in the ability to stimulate lipolysis in isolated hamster adipocytes and corticosterone production in isolated rat adrenal decapsular cells and also in cross-reactivity in an ACTH-specific radioimmunoassay. A portion of the ACTH-like bioactivity and immunoactivity was unadsorbed on the ion exchanger. Opiate-like activity in opiate receptor binding assay, employing [3H]D-ala2-D-leu5 enkephalin or [3H]naloxone as ligand, also resided in fractions adsorbed on CM cellulose. The data indicate a separation of ACTH-like and opiate-like activities, and the presence of opiate-like molecules with different affinities of binding to mu and delta opiate receptors.

Characterization of endorphins from the pituitary of the spiny dogfish Squalus acanthias

Opioid-like immunoreactive material was extracted from the pituitary and brain of the Spiny Dogfish Shark Squalus acanthias. The immunoreactive material in the pituitary extracts was purified to apparent homogeneity by reverse phase high performance liquid chromatography and subsequently characterized by amino acid analysis, Edman degradation and fast atom bombardment mass spectrometry. The largest opioid-like peptide isolated contained 30 amino acids and showed 80 percent homology with salmon endorphin-II but less than 50 percent homology with human beta-endorphin. Three structural variants of this molecule were also characterized. These variants were shown to be shorter N-terminal fragments, two of which corresponded to cleavage products at the single basic residues arginine and lysine. Cleavage at a single lysine residue has not been reported for posttranslational processing of beta-endorphin in mammals and could represent a modification seen only in lower vertebrates. The remaining fragment corresponded to a loss of 3 residues from the C-terminus of the parent molecule. No alpha-N-acetylated peptides were detected. These results provide the first unequivocal confirmation of beta-endorphin in an elasmobranch and provide evidence of novel N-terminal variants of beta-endorphin.

Brain and pituitary beta-endorphin levels at different developmental stages of the rat

beta-Endorphin-like immunoreactivity in whole brains of Sprague-Dawley rat fetuses of different gestational ages was measured by radioimmunoassay and found to increase throughout the gestational period studied. The immunoreactivity in various brain parts (forebrain, midbrain, hindbrain, hypothalamus and pituitary) of late prenatal, early postnatal, young mature and retired breeder rats was also determined. In all the brain parts studied, a maximum in the content and concentration of beta-endorphin-like immunoreactivity was attained when the rats were about 3-4 months old.

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.

Regional distribution of methionine-enkephalin-Arg6-Phe7 in the rat brain: comparative study with the distribution of other opioid peptides

The distribution of the opioid peptide methionine-enkephalin-arginine6-phenylalanine7 (M-Enk-Arg6-Phe7) has been investigated in various structures of the rat brain by using a highly specific radioimmunoassay (RIA). Immunoreactive M-Enk-Arg6-Phe7 has been further characterized by high performance liquid chromatography. The levels of M-Enk-Arg6-Phe7 in various structures of the rat brain were compared with the levels of several other opioid peptides, including methionine-enkephalin (M-Enk), leucine-enkephalin (L-Enk), dynorphin 1-13, and alpha-neoendorphin, which were also measured by RIA. There was a close relationship between the distribution of M-Enk-Arg6-Phe7 immunoreactive material (ir), M-Enk ir, and L-Enk ir. The distribution of dynorphin 1-13 ir and alpha-neoendorphin ir appeared to be distinct from that of the enkephalin group. These results are in agreement with recent reports on the cloning and sequencing of the c-DNA coding for the prohormones, in which it has been hypothesized that M-Enk-Arg6-Phe7 and M-Enk are synthesized by the same precursor, called proenkephalin, and that dynorphin-related peptides and alpha-neoendorphin arise from a separate precursor, prodynorphin.

beta-Endorphin: analgesic and receptor binding activity of non-mammalian homologs

Analgesic potencies of turkey, ostrich and des-acetyl salmon beta-endorphins have been measured in the tail-flick test and binding affinities determined by radio-receptor assay. The duration of analgesia and the slope of the dose-response curves generated by these peptides are similar to those elicited by mammalian beta-endorphins. This suggests that they act in vivo and in vitro on the same population of opiate receptors. The ratio of binding to analgesic potencies observed for these peptides varies nearly sixfold. Structure-activity analysis suggests that a basic side-chain at position 9 is required in order to produce a high opiate activity both in vivo and in vitro. A reexamination of the biological activities of camel beta-endorphin shows that the analgesic potency and binding affinity of this peptide are respectively 171 and 2.7 times higher than human beta-endorphin. His-27 and/or Gln-31 may contribute to this increased potency. The dissociation of radioreceptor binding affinity from analgesic potency in these naturally occurring beta-endorphin homologs suggests that either the conditions under which the binding assay is performed mask the true binding potency in the brain or that, once bound to the appropriate receptor, these homologs do not possess equal ability to produce biological effects.

Selective inhibition of 'motor endplate-specific' acetylcholinesterase by beta-endorphin and related peptides

The effects of beta-endorphin (lipotropin 61-91) and related naturally-occurring peptides upon acetylcholinesterase activity in rat hind-limb muscles was investigated. beta-endorphin weakly inhibited the activity in a plasma membrane-enriched fraction. The inhibition by beta-endorphin of the membrane-associated acetylcholinesterase was less marked when the fractions were prepared from muscles which had been denervated 4-6 days previously. The membrane-associated acetylcholinesterase was solubilised from normal muscle preparations and separated by sucrose density gradient centrifugation into three major peaks (16S, 10S and 4S). beta-Endorphin inhibited the activity in the 16S peak but not that in the 10S and 4S peaks, whilst tensilon, a competitive inhibitor of acetylcholinesterase, inhibited the activity of all three peaks. beta-Endorphin inhibited the activity in the 16S peak but not that in the 10S and 4S peaks, whilst tensilon, a competitive inhibitor of acetylcholinesterase, inhibited the activity of all three peaks. beta-Endorphin inhibited the 16S activity in a concentration-dependent manner and its action was partly prevented if naloxone was added simultaneously. Purified natural porcine and bovine beta-endorphin were equipotent in terms of effective concentration range but the maximum inhibition was greater with the bovine peptide. beta-Lipotropin was approximately 4 times less potent than beta-endorphin, whilst C-fragment (lipotropin 61-87) was 100 times less potent. Prolonged treatment with collagenase did not reduce the catalytic activity of 16S acetylcholinesterase, but it was no longer susceptible to the inhibitory action of beta-endorphin. Kinetic studies indicated a complex type of inhibition by beta-endorphin (hyperbolic Lineweaver-Burke plot). Methionine enkephalin inhibited acetylcholinesterase in a weakly non-competitive manner and its action was not abolished if the enzyme was predigested with collagenase. beta-Endorphin produces a novel form of inhibition of acetylcholinesterase, acting only on the 16S (A12 or 'motor endplate-specific') form of the enzyme. The findings are discussed in the light of evidence that beta-endorphin-related immunoreactivity is expressed in motor nerve axons in the immature rat.

Distribution of beta-endorphin-related peptides in rat pituitary and brain

beta-Endorphin, the most potent known naturally occurring analgesic agent, is found in pituitary and brain in company with a series of structurally and biosynthetically related peptides that are essentially devoid of opiate activity. In studies of beta-endorphin it is important to discriminate between the active and inactive forms of the peptide. This review describes the use of chemical and immunological methods for localizing the peptides in the tissues, extracting and resolving the peptides by chromatography, and determining the concentrations of the peptides by radioimmunoassay. These approaches have allowed the distribution of beta-endorphin and its related peptides to be assigned unequivocally in regions of rat pituitary and brain. It has been found that the multifunctional corticotropin-endorphin prohormone can undergo processing by different mechanisms in different tissues, permitting the intrinsic activities of its fragments to be expressed selectively. The different processing patterns can be attributed to the existence of highly specific enzymes, characteristic of individual cells, which regulate the formation of this potent opiate.

beta-Endorphin: isolation, amino acid sequence and synthesis of the hormone from horse pituitary glands

Beta-endorphin has been isolated from equine pituitaries. Its amino acid sequence is identical to that of ovine, bovine and camel beta-endorphins except for substitution of the threonine residue at position 6 by serine. The equine beta-endorphin has also been synthesized by the solid-phase method. In comparison with the human hormone, equine beta-endorphin was shown to possess 3 times the receptor-binding activity in rat membrane preparations and 1.6 times the analgesic potency in the mouse tail-flick assay.

beta-Lipotropin: primary structure of the hormone from the ostrich pituitary gland

The amino acid sequence of beta-lipotropin from the ostrich pituitary has been determined. It consists of 79 amino acids. The amino acid sequence has been determined as follows: H-(1)AlA-Leu-Pro-Pro-Ala-Ala-Met-Leu-Pro-(10)Ala-Ala-Ala-Glu-Glu-Glu-Glu-Gly-Gl u-Glu-(20)Glu-Glu-Glu-Gly-Glu-Ala-Glu-Lys-Glu-Asp-(30)Gly-Gly-Ser-Tyr-Arg-Met-A rg-His-Phe-Arg-(40)Trp-Gln-Ala-Pro-Leu-Lys-Asp-Lys-Arg-Tyr-(50)Gly-Gly-Phe-Met- Ser-Ser-Glu-Arg-Gly-Arg-(60)Ala-Pro-Leu-Val-Thr-Leu-Phe-Lys-Asn-Ala-(70)Ile-Val -Lys-Ser-Ala-Tyr-Lys-Lys-Gly-(79)Gln-OH. When compared with the primary structures of other known beta-lipotropins, the sequence at the NH2-terminal, beta-melanotropin and beta-endorphin portions of the molecule exhibit considerable variability.

Primary sequence of two regions of mouse pro-adrenocorticotropin/endorphin

The amino acid sequences of two previously uncharacterized regions of the mouse anterior pituitary common precursor to adrenocorticotropin (ACTH) and beta-endorphin (pro-ACTH/endorphin) were determined. Portions of the NH2-terminal region of pro-ACTH/endorphin (called the 16K fragment) and the region between ACTH and beta-endorphin (called gamma-lipotropin) were sequenced by Edman degradations of biosynthetically labeled immunoprecipitated proteins and by Edman degradations of purified 16K fragment and beta-lipotropin. With a combination of these two approaches, 29 of the first 34 residues at the NH2-terminal end of the mouse 16K fragment were determined. The NH2-terminal region of the mouse 16K fragment was found to be nearly identical with the homologous porcine and bovine molecules. The complete amino acid sequence of the NH2-terminal region of gamma-lipotropin was determined. In contrast to the highly conserved nature of the 16K fragment, mouse gamma-lipotropin was found to differ substantially from the gamma-lipotropins of other species. Although the NH2-terminal and beta-melanotropin-like regions of the mouse gamma-lipotropin are similar to the corresponding regions of other gamma-lipotropins, the intervening region of mouse gamma-lipotropin is substantially shorter than it is in other gamma-lipotropins. In addition, mouse gamma-lipotropin lacks the pair of basic amino acids that normally mark the proteolytic cleavage site used to produce beta-melanotropin from gamma-lipotropin.

Isolation and characterization of the bovine corticotropin/beta-lipotropin precursor gene

The entire bovine corticotropin/beta-lipotropin precursor gene has been isolated as a set of overlapping genomic DNA fragments which extend over a length of approximately 17000 base pairs. Restriction mapping of the cloned DNA fragments and nucleotide sequence analysis of the whole mRNA-coding segments and their surrounding regions have established that the corticotropin/beta-lipotropin precursor gene is approximately 7300-base-pairs long and contains two intervening sequences; one with an approximate length of 4000 base pairs is located within the segment encoding the 5'-untranslated region of the mRNA, and the other with an approximate length of 220 base pairs interrupts the protein-coding sequence near the signal peptide region. Sequence analysis of more than 200 base pairs preceding the proximal end of the corticotropin/beta-lipotropin precursor gene has revealed a 'Hogness box' and a variant of the model sequence d(G-G-TC-C-A-A-T-C-T) as well as palindrome structures as observed in other eukaryotic genes. Furthermore, some sequence similarities in the 5'-flanking region are found between the corticotropin/beta-lipotropin precursor gene and the mouse alpha-globin and beta-globin genes, all of which are negatively regulated by glucocorticoids. At least four homologous repetitive sequences are distributed at 3000-5000-base-pair distances in the corticotropin/beta-lipotropin precursor gene region; two such sequences are located in the 5'-flanking region, and one within each intervening sequence. Blot hybridization analysis of bovine pituitary nuclear RNA has indicated that the entire corticotropin/beta-lipotropin precursor gene is transcribed into a primary hnRNA product, which is then spliced to form the mature mRNA.

Isolation, characterization and amino acid sequence of beta-lipotropin from human pituitary glands

Beta-Lipotropin has been purified to homogeneity from human pituitary glands. It consists of 89 amino acids with a molecular weight of 11 700. The lipolytic potency of the human hormone is identical to that of ovine beta-LPH. The amino acid sequence has been determined as follows: (see formula in text). When compared with the structure of the ovine hormone, the sequence at the NH2-terminal 33 residues exhibits considerable variability.

Chemistry and biosynthesis of pro-opiomelanocortin. ACTH, MSH's, endorphins and their related peptides

Studies of lipotropins, melanotropins and endorphins on one hand, and of adrenocorticotropin on the other, has given rise to the concept of a multipotent precursor molecule recently renamed proopiomelanocortin. The preferential sites of cleavage of the precursor to produce its biologically active components are made of pairs of basic amino acid residues as described for the biosynthesis of beta-MSH and pro-insulin. Such structural feature is also found in other pro-hormone molecules. Pulse chase experiments and secretory studies carried out in both anterior and intermediate lobes of rat pituitary glands revealed the transformation of different forms of the precursor into different end-products, the anterior lobe producing preferentially ACTH and beta-LPH while the intermediate produces mainly the alpha-MSH and beta-endorphin. The multiple forms of precursors seem to differ in their carbohydrate content although at least two different gene products are still possible. The presence of similar peptides in the hypothalamus makes it highly probable that neuropeptides are biosynthesized with similar process. Thus the model of beta-LPH precursor, proposed as early as in 1967, is now applicable to the biosynthesis of all other neuropeptides. Major advances in this field are expected in the 1980s.

Synthesis and radioreceptor binding activity of turkey beta-endorphin and deacetylated salmon endorphin

Des-acetylated salmon endorphin and turkey beta-endorphin have been synthesized by the solid-phase method. Relative opiate activities in a radioreceptor binding assay are: human beta-endorphin, 100; des-acetylated salmon endorphin, 169; turkey beta-endorphin, 94. Thus, non-mammalian endorphins can show high activity in a mammalian assay system.

Isolation and characterization of beta-lipotropin from fin whale pituitary glands

The isolation and characterization of beta-lipotropin from fin whale (Balaenoptera physalus) pituitary glands are described. The proposed primary structure is also presented. Fin whale beta-LPH exhibited an identical lipolytic activity when compared with human hormone.

Isolation and characterization of beta-endorphin-like peptides from bovine brains

Four beta-endorphin-like peptides from bovine brain extracts have been identified by their behavior in CM-cellulose chromatography, gel filtration, high-performance liquid chromatography, and radioimmunoassay. Two of them have been isolated in sufficient quantity for amino acid analysis, radioimmunoassay, and radioreceptor assay. One peptide has an amino acid composition nearly identical to that of beta-endorphin with 56% of the radioimmunoreactivity and 2.3% of the potency in the radioreceptor assay of beta-endorphin. The amino acid content of the other beta-endorphin-like peptide is very different from that of bovine beta-endorphin but it has 47% of the radioimmunoreactivity and 1% of the potency in the radioreceptor assay of beta-endorphin.

Nucleotide sequence of cloned cDNA for bovine corticotropin-beta-lipotropin precursor

The nucleotide sequence of a 1,091-base pair cloned cDNA insert encoding bovine corticotropin-beta-lipotropin precursor mRNA is reported. The corresponding amino acid sequence indicates that the precursor protein consists of repetitive units and includes a third melanotropin sequence in its cryptic portion. Pairs of lysine and arginine residues separate the component peptides of the precursor.

Human beta-endorphin. Immunoreactivity of synthetic analogs with various chain lengths

Immunoreactivity of synthetic human beta-endorphin analogs with various chain lengths has been examined using a specific radioimmunoassay. It was found that beta-endorphin-(1--21) and analogs of shortened chain exhibit no immunoreactivity, whereas beta-endorphin-(1--15) possesses significant in vitro opiate activity. It appears that immunoreactivity of beta-endorphin resides in the COOH-terminal segment of residues (22--31). The data also show the lack of correlation between opiate and immunological activities of beta-endorphin.