Opioid peptides isolation

The relatively large number of opioid peptides isolated in recent years is a reflection of the complexity of the endogenous opioid system. The major opioid peptides are cleavage products of three distinct proteins, which are the primary products of three genes. These precursor proteins are proenkephalin... 

The opioid peptides isolated from mammalian tissue are known collectively as endorphins, a word that is derived from a combination of endogenous and morphine. The opioid alkaloids and all of the synthetic opioid derivatives are exogenous opioids. Interestingly, the isolation of morphine and codeine in small amounts has been reported from mammalian brain (9). The functional significance of endogenous morphine remains unknown. 

Figure 9. Diagrammatic representation of the enkephalin-containing (opioid) peptides isolated from bovine adrenal medulla (from Lewis et al., 1980b). The precursor contains both [Met ]enkephalin and [Leu ]enkephalin in an approximate ratio of 7 1. Ovals denote [Met ]-enkephalin squares, [Leu ]enkephalin R, arginine K, lysine F, phenylalanine R/K, arginine or lysine OX, oxidized methionine.

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). 

Endogenous opioid peptides are the wide variety of endogenous peptides isolated since 1975 which are the natural ligands for the opioid receptors. The peptides... 

The third prohormone from which opioid peptides are derived is pro-opiomelanocortin, which yields a number of nonopioid and opioid peptide products (O Donohue and Dorsa 1982). Of these products, beta-endorphin, an untriakontapeptide isolated from camel pituitary gland by Li and Chung (1976)) is thought to interact primarily with mu and delta receptors. 

Since the discovery of the enkephalins in 1975 [11] a large number of endogenous opioid peptides have been detected in mammals, and at present three distinct families of opioid peptides are known (for a review, See Ref. 12). These are the enkephalins, the endorphins (a-, (J-, and y-), and the dynorphins and neoendorphins. The recently discovered endomor-phins [13] also may represent endogenous opioid peptides. Peptides with opioid activity have also been isolated from tryptic digests of milk casein... 

Initial studies of brain delivery based on the chimeric peptide strategy used the absorptive-mediated uptake of cationized albumin which was chemically coupled to the opioid peptide P-endorphin [80] or its metabohcaUy stabilized analogue [D-Ala ]P-endorphin. Tracer experiments in which the chimeric peptide was labelled in the endorphin moiety provided evidence of internalization by isolated brain capillaries and transport into brain tissue in vivo [81]. 

Brandt, V., Teschemacher, H., Henschen, A., Lottspeich, F. Novel opioid peptides derived from casein (beta-casomorphins). I. Isolation from bovine casein peptone, Hoppe-Seyler s Z. Physiol. Chem. 1979, 360, 1211-1216. 

Mattheakis et al., 1994). A library of 1012 DNA molecules was used with E. coli ribosome display utilizing a coupled in vitro transcription-translation system. This library was selected for binding to the monoclonal antibody D32.39, which originally bound dynorphin B, a 13-residue opioid peptide, with 0.29 nM affinity. Five cycles of ribosome display resulted in several different peptides with affinities to the antibody ranging from 7.2 to 140 nM affinity. Yet, a peptide with a sequence similar to dynorphin B was not isolated. 

Fukudome, S. and Yoshikawa, M. 1992. Opioid peptides derived from wheat gluten, their isolation and characterization. FEBS Lett. 296, 107-111. 

It is evident that /3-LPT is not the sole source of endogenous opioid peptides found in the pituitary gland now that dynorphin, an active peptide isolated from this organ as early as 1975, has been characterized.(127) This peptide differs from the /3-endorphins (lower mol wt, more basic, more persistent effect in GPI assay, and resistant to CNBr) and its first 13 residues (established by a microsequencing technique) commence with Leu-enkephalin at the N-terminal. The absence of Met5 accounts for its insensitivity toward CNBr. The synthetic tridecapeptide (12, dynorphin 1-13) and dynorphin itself... 

Hao SL, Takahata O, Iwasaki H (1999) IsobolograpMc analysis of interaction between spinal endomorphin-1, a newly isolated endogenous opioid peptide, tmd Udocaine in the rat formalin test. Neurosd Lett 276 177—180... 

The first two opioid peptides were isolated from pig brain and shown to be active in bioassay systems by Hughes and Kosterlitz in 1975 (Hughes etal., 1975). It was some time later, though, that the precursor proteins for these small peptides were discovered. The first of these to be identified was proopiomelanocortin (POMC). It was not until 1982 that PENK was identified and sequenced in multiple species (Udenfriend and Kilpatrick, 1983). 

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