Pentapeptide enkephalins

For this FAB experiment, a sample of the pentapeptidic enkephalin, Tyr.Gly.Gly.Phe.Leu., dissolved in glycerol was bombarded by xenon atoms. The resulting mass spectrum shows abundant protonated molecular ions at m/z 556. 

Hussain MA, Seetharam R, Wilk RR, Aungst BJ, Kettner CA (1995) Nasal mucosal metabolism and absorption of pentapeptide enkephalin analogs having varying N-terminal amino acids. J Pharm Sci 84 62-64. 

Rigid Geometry Studies of Enkephalin The enkephalins are linear pentapeptides, H-Tyr-Gly-Gly-Phe-Met-NH2 (see Figure 2a.) and H-Tyr-Gly-Gly-Phe-Leu-NH2, which bind to several classes of opiate receptors in the mammalian brain including the same receptor as morphine(26,27). Enkephalins have drawn the interest of theoretical biophysicists for two reasons. First, because of their natural opiate activity, it is hoped that improved analgesics can be developed. Second, as pentapeptides, enkephalins are small enough that the molecule can be examined theoretically without excessive expense of computer time. 

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). 

We have also prepared a propargylic acid derivative of the pentapeptide enkephalin (see below), which was reacted, after cleavage and purification, with Co2(CO)g in solution to yield the Co2(CO)6(alkyne) derivative [31]. Similarly, other Co2(CO)6 alkynyl peptides were synthesized from the preprepared peptide and Co2(CO)g in solution (see Sect. 2.2.2 and the section below on biological activity) [32]. In a related fashion, the Co2(CO)6 moiety can also be introduced C-terminally (see Sect. 2.2.3) or internally (see Sect. 2.2.2). 

C. Enkephalins The pentapeptide enkephalins are the ligand of orphan receptors in brain and are present mostly as precursor form in astrocytes. 

AT-Carboxymethyl dipeptides are obtained by using the Strecker reaction between the amino-group of a dipeptide and an aldehyde. Chiral P-lactam components are used in a synthesis of the pentapeptide enkephalin analogue L-Tyr-D-Ala-Gly-L-Phe-L-Leu. ... 

The major clinical use of opioids is as analgesics for severe pain. Opioids bind to receptors whose endogeneous ligands are peptides such as the pentapeptide enkephalins (H-TVr-Gly-Gly-Phe-Leu-OH and H-Tyr-Gly-Gly-Phe-Met-OH). As with other receptors, there are families of opioid receptors and the major pharmacological division is between the p, K, and... 

In some cases, redundant amino acids may render analysis more complex. In the case of the opioid pentapeptide enkephalin, Tyr-Gly-Gly-Phe-Met, analysis has been aided by the incorporation of stereochemically deuterated glycine residues. Such studies have shown that conformational averaging in the peptide backbone must occur in order to account for the observed spin-spin couplings (Fishman et a/., 1978). 

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."... 

When the compounds of interest are fragile and thermally labile, thermospray Ic/ms is a good choice. Figure 5, shows the thermospray spectmm for leucine enkephalin [58822-25-6] a pentapeptide of molecular weight 555. The Ic/ms approach has been very helpful in unraveling the stmcture of large biological molecules (21). 

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 identification of the morphine receptor spurred an effort in many laboratories to find an endogenous agonist for which that receptor was normally intended. Ultimately, a pair of pentapeptides that bound quite tightly to opiate receptors were isolated from mammalian brains. These peptides, called enkephalins (2, 3), show many of the activities of synthetic opiates in isolated organ systems. They do in fact show analgesic activity when injected directly into the brain. It is thought that lack of activity by other routes of administration is due to their rapid inactivation by peptide cleaving enzymes. 

Enkephalins, pentapeptides found in the central nervous system that are natural analgesics... 

Figure 6 shows the signal response in ESI of Leucine Enkephalin, a pentapeptide, as a function of solvent and additive variation. Although the peptide can be ionized in basic media, acidic pH is much more favorable. This result also confirms that formic acid and acetic acid promote ESI signals far more efficiently than TEA. 

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. 

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 [Leuj-enkephalin (A). The effects of the opioids can be abolished by antagonists (e.g., naloxone A), with the exception of buprenorphine. 

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... 

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