Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01189 (beta-endorphin)
 21,003 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Photo-affinity labelling of MSH receptors on tail-fin melanophores of Xenopus tadpoles with p-azidophenylalanine 13-alpha-MSH (Pap13)-alpha-MSH) or p-azidophenylacetyl-serine1-alpha-MSH ([Apac-Ser1]-alpha-MSH) resulted in a long-lasting stimulation of the melanophores which cannot be reversed despite continuous washing. The generation of this irreversible response is inhibited when photo-affinity labelling is performed in a Ca2+-free medium or in the presence of Ca2+ antagonists. The irreversible stimulation produced in normal medium is completely reversed upon removal of Ca2+ , but is not affected by Ca2+ antagonists or melatonin. Re-addition of Ca2+ after temporary removal restores to irreversible stimulation, even in the presence of Ca2+ antagonists or melatonin. This proves that covalent alpha-MSH-receptor complexes remain fully functional despite temporary deprivation of ca2+. Racemized alpha-MSH, which binds 'tightly' to the receptor and produces a long-lasting effect, is removed from the receptor in Ca2+-free medium, but not by Ca2+ antagonists or melatonin. These results confirm earlier results showing that at least 2 Ca2+ sites are involved in alpha-MSH action, one associated with MSH-receptor binding and the other with the subsequent generation of the effect. The dual role of Ca2+ is not the result of EGTA present; it is specific (Mg2+ has no effect) and is identical for the two different photoreactive alpha-MSH derivatives.
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PMID:Calcium sites in MSH stimulation of xenopus melanophores: studies with photoreactive alpha-MSH. 628 Nov

Calcium ion is essential for normal stimulation of adrenal cortical adenylate cyclase by adrenocorticotropic hormone (ACTH). Both ACTH and Ca2+ act to promote the activation of adenylate cyclase by guanine nucleotides such as guanyl-5'-yl imidodiphosphate [Gpp(NH)p]. To define further the mechanisms by which Ca2+ and ACTH interact with guanine nucleotides, we have correlated the binding of [3H]Gpp(NH)p to adrenal membranes and solubilized membrane proteins with activation of membrane-bound and solubilized adenylate cyclase. Ca2+ increases both the rate of reversible nucleotide binding and the rate of adenylate cyclase activation by nucleotide. This effect is accompanied by the appearance of binding sites having an 8- to 10-fold higher affinity for [3H]Gpp(NH)p. In contrast to Ca2+, ACTH increases the rate of enzyme activation but has no significant effect on nucleotide binding. In Ca2+-depleted membranes, measured nucleotide binding is low, and ACTH has no effect on enzyme activation. Once nucleotide is initially bound, both divalent cations and hormone can promote the transition of the enzyme to an activated state. Mg2+ is more effective than Ca2+ in promoting this transition, while Ca2+ is more effective than Mg2+ in promoting initial nucleotide binding. When membranes containing bound [3H]Gpp(NH)p are solubilized with Lubrol PX, adenylate cyclase activity elutes on Sepharose 4B with an apparent molecular weight of 160,000. The major fraction containing bound nucleotide elutes with an apparent molecular weight of 40,000-50,000. Nucleotide bound to this fraction is increased by pretreatment of the membranes with Ca2+ but is not affected by pretreatment with ACTH. Nucleotide bound to solubilized membrane components dissociates after treatment with EDTA. These findings suggest that Ca2+ promotes the initial binding of Gpp(NH)p to a biologically effective site that may involve a guanine nucleotide regulatory protein. ACTH activates adenylate cyclase by promoting a step subsequent to the binding of guanine nucleotide.
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PMID:Activation of adrenal adenylate cyclase by guanine nucleotides. Promotion of nucleotide binding by calcium but not by adrenocorticotropic hormone. 630 Jun 46

Binding of human beta-endorphin to mouse brain membrane preparations has been characterized using the tritiated hormone as primary ligand. The binding was shown to be time and temperature dependent. The dissociation constant of the saturable binding was determined to be 0.5 nM. Both [Met5]enkephalin and naloxone were found to compete with tritiated beta-endorphin for the binding with a potency of 6.3 and 6.5% of the unlabeled hormone, respectively. Phospholipase A2 isolated from Formosan cobra venom was shown to be a potent inhibitor of the binding with a 50% inhibition concentration of 26 nM. Although Na+, K+, Ca2+, Mg2+ were found individually to exert a profound inhibition on the binding, the combined salt solution (Tyrode) did not abolish the specific binding of tritiated beta-endorphin to the mouse brain membrane preparations.
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PMID:beta-Endorphin: characteristics of binding sites in the mouse brain. 630 56

Effects of the neuropeptide corticotropin-(1-24)-tetracosapeptide (ACTH) on the endogenous and exogenous phosphorylation of lipids and endogenous phosphorylation of proteins were investigated in microsomes and a 110,000 X g supernatant fraction [30-50% (NH4)2SO4 precipitate; ASP 30-50] obtained from rabbit iris smooth muscle. Subcellular distribution studies revealed that both of these fractions are enriched in diphosphoinositide (DPI) kinase. The 32P labeling of lipids and proteins was measured by incubation of the subcellular fractions with [gamma-32P]ATP. The labeled lipids, which consisted of triphosphoinositide (TPI), DPI, and phosphatidic acid (PA) were isolated by TLC. The microsomal and ASP 30-50 fractions were resolved into six and nine labeled phosphoprotein bands, respectively, by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The basal labeling of both lipids and proteins was rapid (30-60 s), and it was dependent on the presence of Mg2+ in the incubation medium; in general it was inhibited by high concentrations (greater than 0.2 mM) of Ca2+. ACTH stimulated the labeling of TPI and inhibited that of PA in a dose-dependent manner, with maximal effect observed at 50-100 microM of the peptide. ACTH appears to increase TPI labeling by stimulating the DPI kinase. Under the same experimental conditions ACTH (100 microM) inhibited significantly the endogenous phosphorylation of six microsomal phosphoproteins (100K, 84K, 65K, 53K, 48K, and 17K). In the ASP 30-50 fraction, ACTH inhibited the phosphorylation of three phosphoproteins (53K, 48K, and 17K) and stimulated the labeling of six phosphoprotein bands (117K, 100K, 84K, 65K, 42K, and 35K).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of corticotropin-(1-24)-tetracosapeptide on polyphosphoinositide metabolism and protein phosphorylation in rabbit iris subcellular fractions. 631 87

Fractions enriched in plasma membranes were prepared from the Y1 mouse adrenocortical tumor cell line and were characterized with respect to adenylate cyclase activity. Optimal requirements of the adenylate cyclase system for guanyl nucleotides. Mg2+, ATP, and corticotropin (ACTH) were determined. The sensitivity of the adenylate cyclase system to ACTH in plasma membrane fractions was comparable with that observed in isolated intact cells. Polycations such as poly-L-arginine and histone competitively inhibited the action of ACTH, supporting the view that the affinity of ACTH for the adenylate cyclase system is determined by the basic core of amino acids at residues 15-18. ACTH was at least one order of magnitude more potent than ACTH in stimulating adenylate cyclase activity in plasma membrane fractions.
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PMID:Adenylate cyclase activity in Y1 mouse adrenocortical tumor cells: some properties of the enzyme associated with purified plasma membrane fractions. 631 50

Pro-opiomelanocortin (ACTH/endorphin prohormone) is processed within the secretory vesicles of pituitary intermediate lobe cells to alpha-melanotropin and beta-endorphin. In order to learn more about the microenvironment in which processing occurs, a method was developed to purify large quantities of bovine intermediate lobe secretory vesicles (ILSV) using isoosmolar metrizamide-sucrose gradients. Analysis of alpha-melanotropin and marker enzymes revealed that the gradients provided a 94-fold purification of secretory vesicles with respect to lysosomes and a 15-fold purification with respect to mitochondria. Pro-opiomelanocortin-converting enzyme activity in the ILSVs was assayed and found to be maximally active around pH 5. From measuring the delta pH across the intact ILSV membrane using 9-aminoacridine fluorescence quenching, the internal pH of ILSVs was determined to be less than 5.6, consistent with the operating pH range of the converting enzyme activity. The pH gradient of the ILSVs collapsed in the presence of ammonium sulfate or by using a combination of nigericin and K+, when the external medium pH was 7. Using the voltage-sensitive dye, oxanol VI, Mg2+ ATP was shown to cause a marked change in the ILSV membrane potential with the inside being positive which was reversed by the proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Thus, the ILSVs appear to have a Mg2+ ATP-dependent electrogenic proton-translocating system.
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PMID:Measurement of delta pH and membrane potential in secretory vesicles isolated from bovine pituitary intermediate lobe. 633 Jan 4

The possibility that divalent cations may antagonize opiate peptide analgesia and stress-induced analgesia was examined. Intracerebroventricular injection of low doses of Ca2+, Mn2+ and Mg2+ antagonized beta-endorphin and methionine-enkephalin analgesia. Ba2+ and Cd2+ were without effect. The ionophore, A23187, significantly antagonized beta-endorphin analgesia and the effect was increased when a low dose of Ca2+ was injected at the same time as the ionophore. Ethylene glycol tetraacetic acid (but not ethylenediamine tetraacetic acid) significantly potentiated endorphin analgesia. Stress-induced analgesia, as determined by increased tail-flick latencies following intraperitoneal injection of acetic acid, was effectively antagonized by naloxone, Ca2+ and Mn2+. The frequency of writhing following acetic acid injection was increased by both naloxone and divalent metal ions, again suggesting antagonism of endogenous opiates. These results confirm previous findings indicating that divalent metal ions (and especially Ca2+) may be involved in the actions of opiates.
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PMID:Modification of endorphin/enkephalin analgesia and stress-induced analgesia by divalent cations, a cation chelator and an ionophore. 682 Nov 93

An aminopeptidase with specificity directed toward peptides with acidic N-terminal amino acid residues has been isolated from mouse brain cytosol. Purification by ion-exchange chromatography and gel filtration resulted in an enzyme that hydrolyzed aspartyl-phenylalanine methyl ester at a rate of 13.2 mumols/min/mg protein at pH 7.5, an increase in specific activity of 1000-fold over that of brain homogenate. Its apparent molecular weight, determined by gel filtration, is approximately 450,000. Dipeptides with N-terminal aspartyl residues are cleaved preferentially to glutamic-containing analogs, and a neutral amino acid (or histidine) is necessary in the adjacent position. For peptides of the form aspartyl-X, relative activity was 100, 81, 71, 66, 19, or 0, where X was alanine, serine, leucine, phenylalanine, histidine, or proline, respectively. Tripeptides were more rapidly hydrolyzed than dipeptides; however, activity tended to decline with increasing chain length. The acidic aminopeptidase can account for almost all of the activity of brain cytosol toward the N-terminal aspartyl residue of angiotensin II, aspartyl-phenylalanine methyl ester or aspartyl-alanine, and the N-terminal glutamyl residue of adrenocorticotropin(5-10). The enzyme was unaffected by bestatin or amastatin. It was inhibited by o-phenanthroline and EDTA. The latter effect could be reversed completely by Zn2+ and partially by Mn2+ or Mg2+; Co2+ and Fe2+ had no effect; Ca2+ was inhibitory. These properties distinguish the brain acidic aminopeptidase from aminopeptidase A isolated from human serum or pig kidney and the aspartyl aminopeptidase of dog kidney.
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PMID:An aminopeptidase from mouse brain cytosol that cleaves N-terminal acidic amino acid residues. 685 30

The conditions in which Leu(5)-enkephalin inhibition of striatal adenylate cyclase was observed were defined. It was determined that enkephalin inhibition was dependent on GTP. The apparent K(m) for GTP in opiate inhibition was determined to be 0.5 and 2 micrometer when 0.1 mM- and 0.5 mM-ATP were used as substrate. ITP, but not CTP or UTP, could substitute for GTP in the reaction. Though the addition of monovalent cations-Na+, K+, Li+, Cs+, and choline+--stimulated striatal adenylate cyclase activity, enkephalin inhibition of striatal adenylate cyclase did not require Na+ when theophylline was used as the phosphodiesterase inhibitor. Under optimal conditions, i.e., 20 micrometer-GTP and 100 mM-Na+, Leu(5)-enkephalin inhibited the strial adenylate cyclase activity by 23-27%. When the enkephalin regulation of the cyclase activity was further characterized, it was observed that Leu(5)-enkephalin inhibited the rate of the enzymatic reaction. Kinetic analysis revealed that the opioid peptide decreases V (max) values but not the K(m) values for the substrates Mg2+ and Mg-ATP. Agents such as MnCl(2), NaF, and guanyl-5'-ylimido-diphosphate, which directly activated the adenylate cyclase, antagonized the opiate inhibition. Levorphanol and (-)naloxone were more potent than dextrorphan and (+) naloxone in inhibiting adenylate cyclase and in reversing the enkephalin inhibition, respectively. There were differences in the potencies of various opiate peptides in their inhibition of striatal adenylate cyclase activity, with Met5- > Leu(5)-enkephalin > beta-endorphin. The opiate receptor through which the enkephalin inhibition was observed is most likely delta in nature, since in the presence of either Na+ or K+, the magnitude of the alkaloid inhibition was reduced, whereas the peptide inhibition was either potentiated or not affected.
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PMID:Demonstration and characterization of opiate inhibition of the striatal adenylate cyclase. 724 Nov 39

The properties of the calcium/calmodulin-dependent protein phosphatase calcineurin and its potential role in stimulus-secretion coupling were examined in AtT20 mouse pituitary corticotrope tumor cells. Protein phosphatase activity was assayed by measuring the liberation of 32P from 32P-casein, adrenocorticotropin secretion was measured by radioimmunoassay. About 60% of the total phosphatase activity was inhibited by 500 nM okadaic acid, suggesting the presence of protein phosphatases 1 and/or 2A. A further 25-30% reduction of phosphatase activity was achieved by chelating free calcium. Addition of the EF-hand protein blocker trifluoperazine or a calcineurin autoinhibitory peptide fragment markedly reduced okadaic acid resistant and calcium-dependent protein phosphatase activity indicating that calcium-dependent 32P release is largely due to calcineurin (protein phosphatase 2B). The remaining 10-15% of total activity was Mg2+ dependent and blocked by NaF, hence possibly due to protein phosphatase 2C. Calcineurin activity was inhibited by the immunosuppressants FK506 and cyclosporin A, either when added to the cell lysates or after preincubation of intact cells with the drugs for 30 min at 37 degrees C. When added to lysates, cyclosporin A inhibited calcium/calmodulin-dependent phosphatase more effectively than FK506. However, when tested on intact cells, FK506 proved 10-fold more potent than cyclosporin A. Both immunosuppressive agents enhanced the calcium-dependent release of adrenocorticotropic hormone into the medium, once more, FK506 was 10-fold more potent than cyclosporin A. Taken together, these data suggest that calcineurin is an inhibitory element in the signal transduction pathway controlling exocytotic secretion in pituitary cells that express voltage-operated calcium channels. This is in direct contrast with leukocytes where voltage-operated calcium channels are not found, and calcineurin is an important element for agonist-induced activation.
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PMID:Inhibitory role for calcineurin in stimulus-secretion coupling revealed by FK506 and cyclosporin A in pituitary corticotrope tumor cells. 768 29


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