Purification and assay of opioid activity of low molecular weight enkephalin-immunoreactive peptides generated by peptic digestion of rat plasma proteins.
A low molecular weight Methionine enkephalin-immunoreactive peptide (MEIP) and two Leucine-enkephalin immunoreactive peptides (LEIP) generated by peptic digestion of rat plasma were purified through gel filtration followed by five sequential reverse phase HPLC gradients in different solvent systems. Binding experiments of these peptides to opioid receptors of rat brains were performed. The two LEIPs were able to inhibit binding of [3H]naloxone to opioid receptors in rat brain membranes. No inhibition was found with the MEIP (which represented the only MEIP present in the low molecular weight fraction of pepsin-digested rat plasma). Sequencing revealed that the MEIP is a six residue peptide with the following sequence: Gly-Glu-Tyr-Gly-Phe-Gln. This sequence corresponds to that of residues 422-427 of rat serum albumin.
Shen
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Department of Biochemistry and Molecular Biology, LSU Medical Center, New Orleans 70112.
Lindberg
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D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004743:Enkephalin, Leucine / Q000032:analysis / Q000302:isolation & purification*; D004744:Enkephalin, Methionine / Q000032:analysis / Q000302:isolation & purification*; D009842:Oligopeptides / Q000032:analysis; D010434:Pepsin A / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism
D000596:Amino Acids; D001798:Blood Proteins; D009842:Oligopeptides; D011957:Receptors, Opioid; D004744:Enkephalin, Methionine; D004743:Enkephalin, Leucine; D010434:Pepsin A