Proteolytic conversion of oxytocin by brain synaptic membranes: role of aminopeptidases and endopeptidases

Peptides. 1991 Sep-Oct;12(5):1119-25. doi: 10.1016/0196-9781(91)90068-z.

Abstract

The proteolytic conversion of oxytocin and vasopressin by purified rat brain synaptic membranes was studied at 37 degrees C and physiological pH 7.4. The formed peptide fragments were isolated by high performance liquid chromatography and characterized by amino acid analysis. When oxytocin was incubated with synaptic membranes, either C- or N-terminal fragments were found. The most abundant were [Cyt6]oxytocin(4-9), [Cyt6]oxytocin(3-9), [Cyt6]oxytocin(2-9), oxytocin(1-8) and oxytocin(1-7). In contrast, only C-terminal fragments, [Cyt6-Arg8]vasopressin(4-9), [Cyt6-Arg8]vasopressin(3-9) and [Cyt6-Arg8]vasopressin(2-9), were found by incubating [Arg8]vasopressin. The formation of C-terminal oxytocin and vasopressin fragments was inhibited by the aminopeptidase inhibitors amastatin and bestatin, while the formation of oxytocin(1-7) and (1-8) was inhibited by the divalent cations Hg(2+) and Zn(2+). The formation of oxytocin(1-7) was also partially prevented by the endopeptidase inhibitor phosphoramidon. The formation of both C- and N-terminal fragments was inhibited by o-phenanthroline. The results suggest that, while [Arg8]vasopressin is metabolized only by membrane-bound aminopeptidases, oxytocin is also metabolized by membrane-bound endopeptidases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acids / analysis
  • Aminopeptidases / metabolism*
  • Animals
  • Brain / enzymology*
  • Chromatography, High Pressure Liquid
  • Endopeptidases / metabolism*
  • Male
  • Molecular Sequence Data
  • Oxytocin / metabolism*
  • Peptide Fragments / isolation & purification
  • Protease Inhibitors / pharmacology
  • Rats
  • Rats, Inbred Strains
  • Synaptic Membranes / enzymology*
  • Vasopressins / metabolism

Substances

  • Amino Acids
  • Peptide Fragments
  • Protease Inhibitors
  • Vasopressins
  • Oxytocin
  • Endopeptidases
  • Aminopeptidases