Fig. 2. Hydrolysis of PDF by recombinant human neprilysin and D. melanogaster head membranes. Peptide fragments generated after incubation of PDF with either (A) neprilysin (1.25 ng) or (B,C) D. melanogaster head membranes (1 µg protein) were separated by HPLC with the UV-monitor set at 214 nm (0.2, full scale absorbance units). The identities of the metabolites PDF1-7 and PDF8-18 were established by mass spectrometry as described in Materials and methods. (C) Pre-incubation of the membranes with 10 µmol l^–1 phosphoramidon abolished the PDF-degrading activity (I, inhibitor peaks).