Degradation of the neuropeptide proctolin by membrane bound proteases 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. Phenanthroline, actinonin, amastatine, bestatin, and (2S,3R)‐3‐amino‐2‐hydroxy‐4‐(4‐nitrophenyl)‐butanoyl‐L‐leucine (HNBL) were tested at the concentration of 0.1 mM at pHs 8.2 and 6 and their ability to prevent the degradation of proctolin was estimated. A 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. Furthermore, the use of these inhibitors confirmed the importance of carboxypeptidase activity at pH 6. These data are the first to describe proctolin degradation in ovary and hindgut muscle, important targets of proctolin action.