Generation of met-enkephalin arg6phe7 immunoreactivity by proteolytic cleavage of mammalian plasma precursors by pepsin

Andrew S. Giraud, Lorraine Parker, Coral Reichman, Mary Familari, A. Ian Smith, John Funder

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A region-specific antiserum raised against the C-terminal heptapeptide of proenkephalin A (Met-enk Arg6Phe7) was used in RIA studies to show that rat, human, and ovine plasma contain substrates (mol wt, 68K) that yield nanomolar amounts of Met-enk Arg6Phe7 (ME-RF) after treatment with pepsin under acid conditions. This ovine plasma-derived immunoreactivity diluted in parallel to the ME-RF standard in RIA and chromatographed as two low mol wt species (∼ IK) which were less hydrophobic than the standard on size exclusion and reverse phase chromatography. The pepsin-generated material displaced [3H]naloxone from rat brain binding sites; its potency was about 1000-fold that of ME-RF, assuming near 100% cross-reactivity with the antiserum. Taken together these observations suggest that the pepsin-generated material is of similar mol wt and amino acid sequence to ME-RF, but differs with respect to opiate-binding efficacy, and that the plasma precursor is distinct from proenkephalin in both size and processing sites.

Original languageEnglish
Pages (from-to)1711-1716
Number of pages6
Issue number4
Publication statusPublished - 1 Jan 1989
Externally publishedYes

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