Peptide 3-endorphin

Three precursor proteins of O. p. have been identified and sequenced. The first, preproopiomelanocortin, is the source of corticotropin (ACTH) and -lipo-tropin (see Hormones). These hormones are cleaved to smaller peptides 3-endorphin is released from P-li-potropin. The second and third precursors are preproenkephalins A and B (PPE A and PPE B). PPE A contains four copies of Met-enkephalin, one of Leu-enkephalin, and two extended Met-enkephalins with six and seven amino acids, respectively. It is also the source of adrenorphin, and other active peptides. PPE B is the precursor of a-neo-endorphin, dynorphin, and PH-8P (a predominant O.p. in brain). 

Goldstein A. Opioid peptides (endorphins) in pituitary and brain. Science 1976 193 1081-1086. 

The opioids produce analgesia by binding to various opioid receptors in the brain, brainstem, and spinal cord, thus mimicking the effects of endogenous opioid peptides (endorphins). Opioids appear to affect both the sensation of noxious stimulation (pain) and the emotional component of subjective distress (suffering). 

Endogenous opioid peptides (endorphins, dynor-phins, enkephalins), have been termed the brain s own morphine. Their discovery in 1972 explained why the brain has opioid receptors when there were no opioids in the body. These peptides attach to specific opioid receptors, mainly p (mu), 5 (delta) or K (kappa) located at several spinal and multiple supraspinal sites in the CNS. Opioid receptors are part of the family of G-protein-coupled receptors (see p. 91) and act to open potassium channels and prevent the opening of voltage-gated calcium channels which reduces neuronal excitability and inhibits the release of pain neurotransmitters, including substance P. 

Transmitters include most amines (ACh, DA, NE, 5HT) and peptides (endorphins). 

Figure 33 Cleavage of pro-opiomelanocortin (POMC) into endorphin and non-opioid peptides. POMC serves as a precursor (pro-) for the opiate peptide, -endorphin (-opio-) for a-, J3- and y-melanocyte-stimulating hormone (MSH, -melano-) for adrenocortkotrophic hormone (ACTH, -cort-) and for a- and /3- lipotropin (-in). Notice that the peptides are not located end-to-end, but that some of the smaller peptide sequences are embedded in larger sequences (e.g., a-lipotropin, P-MSH and P-endorphin are contained within P-lipotropin). Two other protein precursors contain enkephalins and dynorphins. Proenkephalin contains seven met-enkephalin sequences (Tyr-Gly-Gly-Phe-Met). Prodynorphin contains three leu-enkephalin sequences (Tyr-Gly-Gly-Phe-Leu) and the sequences for dynorphin A, Dynorphin B, a-neodynorphin and P-neoendorphin.

POMC) yields ACTH and another glycoprotein, P-Upoprotein (Fig. 3.5). P-lipoprotein further converts to the endogenous opioid peptide endorphin. Likewise, melanocyte stimulating hormone (MSH) results from the cleavage of ACTH. 

Myelin basic protein tryptic peptides -Endorphin fragments Parathyroid hormone Wheat proteins... 

The work flow for dPLIMSTEX starts with half the volume of an equilibrated protein-peptide complex for measurement. The other half is diluted in aqueous buffer before incubation (Figure 11.5). The dilution step is continued until the concentration of the peptide is too low to be detected. dPLIMSTEX was first demonstrated by using a model system, calcium-saturated calmodulin with the opioid peptide )-endorphin it yielded a similar binding constant as that determined by standard PLIMSTEX and other methods. dPLIMSTEX was then applied to a monoclonal antinitro-tyrosine antibody, in complex with a 3-nitrotyrosine-modified peptide system. A binding stoichiometry of 1 2 was confirmed. In addition, a in the low nM range and a minimum of five amino... 

P-Endorphin. A peptide corresponding to the 31 C-terminal amino acids of P-LPH was first discovered in camel pituitary tissue (10). This substance is P-endorphin, which exerts a potent analgesic effect by binding to cell surface receptors in the central nervous system. The sequence of P-endorphin is well conserved across species for the first 25 N-terminal amino acids. Opiates derived from plant sources, eg, heroin, morphine, opium, etc, exert their actions by interacting with the P-endorphin receptor. On a molar basis, this peptide has approximately five times the potency of morphine. Both P-endorphin and ACTH ate cosecreted from the pituitary gland. Whereas the physiologic importance of P-endorphin release into the systemic circulation is not certain, this molecule clearly has been shown to be an important neurotransmitter within the central nervous system. Endorphin has been invaluable as a research tool, but has not been clinically useful due to the avadabihty of plant-derived opiates. 

Biosynthesis. Three separate genes encode the opioid peptides (see Fig. 1). Enkephalin is derived from preproenkephalin A, which contains six copies of Met-enkephalin and extended peptides, and one copy of Leu-enkephalin (62—66). ( -Endorphin is one of the many products of POMC, and represents the N-terminal 31 amino acids of P-Hpotropin (67,68). Three different dynorphin peptides are derived from the third opioid gene, preproenkephalin B, or preprodynorphin (69). The dynorphin peptides include dynorphin A, dynorphin B, and a-neo-endorphin. 

At the time of the discovery of Met-enkephalin, its sequence was observed to be identical to that of residues 61—65 contained in the C-fragment of the pituitary hormone p-Hpotropin [12584-99-5] (p-LPH) (see Hormones), first isolated in 1964 (11). In 1976, the isolation of a larger peptide fragment, P-endorphin [60617-12-1] that also displayed opiate-like activity was reported (12). This peptide s 31-amino-acid sequence comprised residues 61—91 of P-LPH. Subsequentiy, another potent opioid peptide, dynorphin [72957-38-17, was isolated from pituitary (13). The first five amino acids (qv) of this 17-amino-acid peptide are identical to the Leu-enkephalin sequence (see Table 1). 

In addition to the weU-defined opioid systems in the central nervous system, the three opioid peptides and their precursor mRNA have also been identified in peripheral tissues. ( -Endorphin is most abundant in the pituitary, where it exists in corticotroph cells with ACTH in the anterior lobe and in melanotroph cells with MSH in the intermediate lobe (59). Enkephalin and pre-pro-enkephalin mRNA have been identified in the adrenal medulla (60) and this has been the source of material for many studies of pro-enkephalin synthesis and regulation. Pre-pro-enkephalin mRNA has also been identified in the anterior and posterior lobes of the pituitary (61). mRNA for all three opioid precursors has been identified in the reproductive system (62—64). POMC... 

The opioid peptides vary in their binding affinities for the multiple opioid receptor types. Leu- and Met-enkephalin have a higher affinity for 5-receptors than for the other opioid receptor types (68), whereas the dynorphin peptides have a higher affinity for K-sites (69). P-Endorphin binds with equal affinity to both p- and 5-receptors, but binds with lower affinity to K-sites (70). The existence of a P-endorphin-selective receptor, the S-receptor, has been postulated whether this site is actually a separate P-endorphin-selective receptor or is a subtype of a classical opioid receptor is a matter of controversy (71,72). The existence of opioid receptor subtypes in general is quite controversial although there is some evidence for subtypes of p- (73), 5-(74), and K-receptors (72,75), confirmation of which may be obtained by future molecular cloning studies. 

Dynorphin may also influence nociception at the spinal level. The levels of prodynorphin mRNA and immunoreactive dynorphin increase in the chronic inflammatory arthritic model (158). Dynorphin also inhibits morphine or P-endorphin-induced analgesia in naive animals and enhances analgesia in tolerant animals, indicating that this peptide may have a regulatory role in opioid analgesia (159). This effect does not appear to be mediated by a classical opioid receptor, since des-tyrosine dynorphin, which does not bind to opioid receptors, also antagonizes morphine analgesia (160). 

Litde is known about metaboHc inactivation of ( -endorphin and the dynorphins. NEP, and to a lesser extent APN, are only weaMy active against P-endorphin (183). Enzymes are known which degrade P-endorphin in vitro under nonphysiological conditions (202) or which inactivate P-endorphin by N-acetjlation (203). Alack of specific degradative enzymes for these peptides may account for their relatively long half-life in vivo though this has not been definitively estabUshed. 

Endorphins belong to the group of endogenous opioid peptides. 

Proopiomelanocortin (POMC) is the precursor peptide of hormones and neuropeptides expressed in the pituitary and the hypothalamus (adrenocorticotropic hormone (ACTH), lipotropin, a-melanocyte-stimulating hormone (aMSH), yMSH, 3-endorphin, and others). The main clinical consequences of POMC deficiency are adrenal insufficiency (due to absence of ACTH), red hair pigmentation (due to absence of MSH) and severe early-onset obesity (due to the lack of aMSH). 

The basic polymer appears to be a hydroxylated polyether to which octadecyl chains have been bonded and so it behaves as a reverse phase exhibiting dispersive interactions with the solutes. An example of the separation of a series of peptides is shown in figure 15. The column was 3.5 cm long, 4.6 mm i.d. The solutes shown were (1) oc-endorphin, (2) bombesin, (3) y-endorphin, (4) angiotensin, (5) somatostatin and (6) calcitonon. The separation was carried out with a 10 min linear program from water containing 0.2% trifluoroacetic acid to 80% acetonitrile. 

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