Proteolytic conversion of oxytocin by brain synaptic membranes: role of aminopeptidases and endopeptidases.
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.
Stancampiano
R
R
Bernard B. Brodie Department of Neurosciences, University of Cagliarl, Italy.
Melis
M R
MR
Argiolas
A
A
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000626:Aminopeptidases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D010121:Oxytocin / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013570:Synaptic Membranes / Q000201:enzymology*; D014667:Vasopressins / Q000378:metabolism
D000596:Amino Acids; D010446:Peptide Fragments; D011480:Protease Inhibitors; D014667:Vasopressins; D010121:Oxytocin; D010450:Endopeptidases; D000626:Aminopeptidases