Enkephalin analogs modified in the aromatic ring of the N-terminal tyrosine residue
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Leu-enkephalin
Met-enkephalin
Residue (chemistry)
Met-enkephalin
Pentapeptide repeat
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Four analogs of Met-enkephalin were synthetized using DPPA method. Their analgesic activity was estimated by the hot plate method, the neurotoxic effect being also determined. One of the analogs was 16 times as potent as Met-enkephalin, whereas with the three remaining the neurotoxic effect preceded the expected analgesic activity.
Met-enkephalin
Leu-enkephalin
Opiate
Endorphins
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Leu-enkephalin
Met-enkephalin
Residue (chemistry)
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This study examined effects on memory formation produced by [Leu]enkephalin and [Met]enkephalin administration in 2 regions of the 2-day-old chick brain involved in memory formation: the intermediate medial hyperstriatum ventrale (IMHV) and the lobus parolfactorius (LPO). Basal concentrations of endogenous [Leu]enkephalin and [Met]enkephalin were determined for 5 brain regions, and effects of 1-trial peck-avoidance training on enkephalin concentrations were examined in the IMHV and LPO. [Leu]enkephalin was amnestic when administered in the IMHV but not in the LPO. In contrast, [Met]enkephalin may be amnestic when administered in the LPO but not in the IMHV. Training decreased [Met]enkephalin concentration in the LPO but not in the IMHV. Training had no effect on [Leu]enkephalin concentration in either the IMHV or the LPO. Thus, amnestic effects of [Leu]- or [Met]enkephalin administration are brain-region specific. Regional activity of endogenous [Met]enkephalin during memory formation is consistent with localized amnestic effects produced by [Met]enkephalin administration.
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Abstract Immunohistochemical methods have been used to investigate the distribution of various opioid peptides derived from mammalian proenkephalin in the central nervous system of Scyliorhinus canicula. The results indicate that both Leu‐ and Met‐enkephalin‐immunoreactive peptides are present in the dogfish brain. In contrast, enkephalin forms similar to Met‐enkephalin‐Arg‐Phe or Met‐enkephalin‐Arg‐Gly‐Leu, and mammalian α‐neo‐endorphin, dynorphin A (1–8), dynorphin A (1–13), and dynorphin A (1–17) were not detected. Met‐ and Leu‐enkephalin immunoreactivities were found in distinct neurons of the telencephalon and hypothalamus. In particular, cell bodies reacting only with the Met‐enkephalin antiserum were localized in the preoptic nucleus and in the suprachiasmatic region of the hypothalamus. Conversely, cell bodies reacting only with the Leu‐enkephalin antiserum were localized in the pallium and the nucleus lobi lateralis hypothalami. Several areas of the telencephalon and diencephalon exhibited both Met‐ and Leu‐enkephalin‐like immunoreactivity, but the two immunoreactive peptides were clearly contained in distinct perikarya. The overall distribution of Met‐enkephalin‐immunoreactive elements in the dogfish brain exhibited similarities to the distribution of proenkephalin‐derived peptides previously reported for the brain of tetrapods. The fact that Met‐ and Leu‐enkephalin‐like peptides were detected in distinct neurons, together with the absence of dynorphin‐related peptides, suggests the existence of a novel Leu‐enkephalin‐containing precursor in the dogfish brain. © 1994 Wiley‐Liss, Inc.
Proenkephalin
Scyliorhinus canicula
Leu-enkephalin
Met-enkephalin
Diencephalon
Dynorphin
Dynorphin A
Preoptic area
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1. Intrathecal injection of Met-enkephalin (200, 400 and 800 nmol) in rats produced a dose-dependent analgesic effect. That the effect of electroacupuncture (EA) analgesia could be markedly potentiated by ivtrathecal injection of bestatin or thio-phan, the enkephalin degrading enzyme inhibitors, and attenuated by the Met-enkephalin. antiserum strongly suggest the importance of endogenous Met-enkephalin in the pain modulatory system.2. Intrathecal injection of Leu-enkephalin 800 nmol produced only a slight increase of tail flick latency (44±13%) comparable to 200 nmol of Met-enkephalin (61±27%). No significant analgesic effect was seen when Met-enkephalin-Arg6-Phe7 (MBAP) 10-200 nmol was injected intrathecally to the rat. The effect of EA analgesia was not significantly attenuated by intratbecal injection of antisera against Leu-enkephalin or MEAP, nor was it potentiated by captopril (240 nmol), the inhibitor of the HEAP degrading enzyme. All these evidences seem to point to the conclusion that Leu-enkephalin and MEAP in the spinal cord may not play important role in the modulation of pain perception.
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Abstract. To elucidate whether or not human phaeochromocytoma contains methionine-enkephalin-Arg 6 -Gly 7 -Leu 8 (Met-enkephalin-Arg-Gly-Leu) and methionine-enkephalin-Arg 6 -Phe 7 (Met-enkephalin-Arg-Phe) together with methionine-enkephalin (Met-enkephalin) and leucine-enkephalin (Leu-enkephalin), all of which are known to exist in the same precursor molecule (preproenkephalin A), we examined extracts from 16 phaeochromocytomas using high performance liquid chromatography (HPLC) and gel exclusion chromatography coupled with radioimmunoassays (RIAs) for these four opioid peptides. Met-enkephalin-Arg-Gly-Leu-like immunoreactivity (-LI) and Met-enkephalin-Arg-Phe-LI existed together with Met-enkephalin-LI and Leu-enkephalin-LI in 16 phaeochromocytomas. There was a wide variation in contents of Met-enkephalin-LI, Leu-enkephalin-LI, Met-enkephalin-Arg-Gly-Leu-LI and Met-enkephalin-Arg-Phe-LI. Significant positive correlations were observed among the contents of these four opioid peptides in 16 phaeochromocytomas. HPLC and gel exclusion chromatography followed by the RIAs showed the presence of Met-enkephalin, Leu-enkephalin, Met-enkephalin-Arg-Gly-Leu and Met-enkephalin-Arg-Phe together with their high molecular weight forms, which existed in variable amounts. Molar ratios of the contents of these four opioid peptides determined after HPLC varies from case to case. These results indicate the co-existence of Met-enkephalin, Leu-enkephalin, Met-enkephalin-Arg-Gly-Leu and Met-enkephalin-Arg-Phe in human phaeochromocytomas, suggesting the preservation of amino acid sequences of these four opioid peptides even in neoplastic tissues. Evidence for some abnormalities in the posttranslational processing of preproenkephalin A to these four opioid peptides was obtained in certain phaeochromocytomas.
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Met-enkephalin
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Leu-enkephalin
Met-enkephalin
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Veratridine
Met-enkephalin
Leu-enkephalin
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