Degradation of the neuropeptide proctolin by membrane bound protease of the hindgut and ovary of Locusta migratoria and the effects of different inhibitors

Proctolin was incubated in vitro with crude membrane preparations derived from hind gut and ovary of Locusta migratoria . The metabolites of proctolin were separated and identified by reversed phase-high performance liquid chromatography which allowed the determination of the time course of degradation. At pHs 9.2 and 7.4, aminopeptidase activity predominated but some evidence of a carboxypeptidase could be inferred. At pH 6, aminopeptidase activity was slightly reduced compared to the level of aminopeptidase activity at the two former pHs; by contrast the carboxypeptidase was more important. At this pH, the presence of a membrane bound endopeptidase was detected. At both pHs, HNBL and amastatin were revealed to be the most efficient inhibitors (50 to 75% inhibition) and o-phenanthroline appeared particularly efficacious at pH 6 (70% inhibition), whereas it was relatively poor inhibitor at pH 8.2.