Pentapeptide Leu-enkephalin

An example qualification test for CE—MS involves the simple separation of two small pentapeptides Leu-enkephalin (miz 556) and Met-enkephalin (mlz 589). The sample mixture is composed of 100 pmol/pL of each component in 100% H20,1% acetic acid. The CE column is a 50 im ID x 65—80cm bare fused silica pre-washed with O.IM NaOH and H2O, and then pre-rinsed with the running buffer solution of 100% water, 1% acetic acid. The injection method is pressure at 50mbar for 10 s and an ESI sheath liquid in the ratio of 60/40 IPA/water, 1% acetic acid at 2 tL/min. The spectra are collected every 3 s over a 350—3000 mlz scan. 

Langoth et al. [86] studied the properties of matrix-based tablets containing the novel pentapeptide leu-enkephalin (Tyr-Gly-Gly-Phe-Leu) that has been shown to have pain-modulating properties. The matrix-based tablets were made with the thiolated polymer PCP. The covalent attachment of cysteine to the anionic polymer PCP leads to an improvement of the stability of matrix tablets, enhances the mucoadhesive properties, and increases the inhibitory potency of PCP towards buccal enzymes. All these factors lead to stability of the peptide and a controlled drug release for the peptide was obtained for more than 24 h. Also, the tablets based on thiolated PCP remained attached on freshly excised porcine mucosa 1.8 times longer than the corresponding unmodified polymer. 

Figure 3.19. Amino Acid Sequences Flave Direction. This illustration of the pentapeptide Tyr-Gly-Gly-Phe-Leu (YGGFL) shows the sequence from the amino terminus to the carboxyl terminus. This pentapeptide. Leu-enkephalin, is an opioid peptide that modulates the perception of pain. The reverse pentapeptide, Leu-Phe-Gly-Gly-Tyr (LFGGY), is a different molecule and shows no such effects.

Figure 5.49. Sections from the DQF-COSY spectrum of the pentapeptide Leu-enkephalin 5.4. The 2D crosspeaks and the f2 ID trace taken through these correspond to correlations within the tyrosine (Y) residue. The upper trace is taken from the conventional ID spectrum in which the P-proton resonances partially overlap with those of phenylalanine (F). The original 2D data had an f2 resolution of 1.8 Hz/pt but the ID trace was treated as described in the text to yield a final resolution of 0.4 Hz/pt.

The primary structure of peptides (oligopeptides and polypeptides) is described as a linear sequence consisting of the 20 naturally occurring L-amino acids. These amino acids are linked together by amide bonds. Fig. 33 illustrates this for the pentapeptide Leu-enkephalin. 

Synthesis of opioid pentapeptides, Leu-enkephalin and Met-enkephalin by solution methods and their biological activities... 

Hiraoki et al. investigated the phenyl ring dynamics of poly(L-phenylalanine) using H-NMR, showing that it is characterized by a fairly broad distribution of correlation times. The mean correlation time of this distribution was 1.2 x 10 Hz at 25°C, which is close to that of the fast motional component of the B. mori and S.c. ricini silk fibroins. The Tyr ring flip in the pentapeptide [Leu ] enkephalin was reported to be 5.6 x 10 Hz at 25°C, which is close to that of the slow motional component observed here for silk fibroin. On the other hand, the ring motion in crystalline N-acetyl-L-Asp-L-Pro-L-Tyr-N -methylamide was found to be 1.1 X 10 Hz at 27°C, close to that of the fast motional component of the silk fibroins. 

Figure 231. The CPMG sequence performed on the pentapeptide Leu-enkephalin 2.2 in DMSO. Hie faster decay of the amide protons (left) relative to the aromatic protons of the tyrosine residue (right) results from the amide protons coupling to quadmpolar (Section 2.5). The very fast decay of the highest frequency amide proton occurs because this is in rapid chemical exchange with dissolved water, broadening the resonance significantly. The numbers show the total T2 relaxation period 2xn.

Evidence soon emerged that the endogenous opioids were peptides rather than simple morphine-like molecules (9). The first direct evidence for endogenous opioids in brain extracts was provided in 1975 when two pentapeptides were purified that differed only in the carboxyl terminal amino acids (10) (Table 1). These peptides were called methionine- (Met-) and leucine- (Leu-) enkephalin, from the Greek term meaning "in the head."... 

The pentapeptides, met- and leu-enkephalin, have been detected in rat striatum tissue by LCEC at a glassy carbon electrode These peptides can be detected directly... 

The isolation of such endogenous opiates was reported simultaneously by four laboratories those of Goldstein in Palo Alto, Hughes in Aberdeen, Snyder in Baltimore, and Terenius in Uppsala. Acetone extracts of pig, calf, and rat brains yielded, after purification, two pentapeptides, called enkephalins, with the structures NHj-Tyr-Gly-Gly-Phe-Met-COOH (5.83, Met-enkephalin) and NHj-Tyr-Gly-Gly-Phe-Leu-COOH (5.84, Leu-enkephalin). These are present in a 4 1 ratio in pig brain but in a 1 4 ratio in cattle... 

Three families of endogenous opioid peptides have been described in detail the endorphins, the pentapeptide enkephalins methionine-enkephalin (met-enkephalin) and leucine-enkephalin (leu-enkephalin), and the dynorphins. The three families of opioid receptors have overlapping affinities for these endogenous peptides (Table 31-1). 

While morphine as a component of opium has been in use for centuries and the first synthetic opioid, pethidin, was prepared as early as 1939, opioid peptides, the endogenous pentapeptides Met- and Leu-enkephalin (YGGFM and YGGFL), were identified in brain extracts only in 1975 by Kosterlitz and Waterfield (Hughes et al., 1975 also see Cox et al., 1975 Hughes, 1975 Lord et al., 1977). 

Endogenous opioid peptides. Extensive processing is also involved in formation of analgesic opioid peptides, which are present naturally in the brain (see also Section B). Tire formation of (1-endorphin in the hypothalamus from prepro-opiomelanocortin (Fig. 30-2) has already been mentioned. Prior to the discovery of P-endorphin, the pentapeptides Met-enkephalin and Leu-enkephalin (Table 30-4) were discovered and were found to compete with opiate drugs for receptors in the brain. Tire larger P-endorphin, which contains the Met-enkephalin sequence at its N terminus, is a far more potent opiate antagonist than are the enkephalins. Since the Met-enkephalin sequence within P-endorphin is not flanked by basic residues, it apparently is normally not released. Two other recently discovered brain peptides are endomorphin-1 (YPWF-NH2) and endomorphin-2 (YPFF-NH2). They are also potent agonists for the opioid receptors, especially the p receptor (see Section B,10).,61a,61b... 

Schofield et alJ174l described their approach to the oxazabicyclo[4.3.0]nonanone 142 (Scheme 55), as part of an approach to mimic Leu-enkephalin. Template 142 was incorporated into the pentapeptide sequence, replacing the -Gly-Phe- sequence, to provide 143. No biological data were reported. 

The first endogenous ligands for the opioid receptors were isolated by Kosterlitz and Hughes and were found to be the pentapeptides methionine and leucine enkephalin (meta- and leu-enkephalin). The structures of these,... 

Endorphins are peptides produced by the intermediate pituitary that react with the brain s opioid receptors and presumably act as endogenous analgesics. The two best known endorphins from bovine brain are the pentapeptides, met-enkephalin and leu-enkephalin, whose structures are Tyr-Gly-Gly-Phe-Met and Tyr-Gly-Gly-Phe-Leu, respectively. There is evidence that the enkephalins, MSH, and ACTH are produced from the same precursor protein, pro-opiomelanocortin, molecular weight (MW) 31,000. This protein is present in both the anterior and intermediate pituitary glands. In the anterior pituitary area, this protein loses the element of ACTH (39 amino acids). In the intermediate pituitary, this protein... 

Endogenous opioids are peptides that are cleaved from the precursors, proenkephalin, pro-opiomelanocortin, and prodynorphin. All contain the amino acid sequence of the pentapeptides [Met]- or [Leu]-enkephalin (A). The effects of the opioids can be abolished by antagonists (e. g., naloxone A), with the exception of buprenorphine. 

Aminoindane and related ring systems have also been employed as conformational restraints of enkephalins. The analog 24 in which 1-aminoindane replaces residues 4 and 5 of the pentapeptide retains half the GPI activity of DADL,(45) while the peptide 25 modified at the Tyr residue exceeds Leu-enkephalin in potency seven to eight times, but is 30 times less effective at MVD sites.(183) The last derivative showed no activity in mice, using the... 

Enkephalins are endogenous pentapeptides. Two enkephalins have been identified Met-enkephalin and Leu-enke-phahn. Both enkephalins are relatively weak analgesics, which activate all opioid receptors, but appear to have the highest affinity for the delta-receptors. In the CNS, enkephalins have been found in many areas but predominantly those associated with nociception (Przewlocki and Przewlocka, 2001). 

Problem 28.1 7 Draw the structure of leu-enkephalin, a pentapeptide that acts as an analgesic and opiate, and has... 

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