HYDROLYSIS OF INSECT NEUROPEPTIDES BY AN ANGIOTENSIN-CONVERTING ENZYME FROM THE HOUSEFLY, MUSCA-DOMESTICA

The presence in insect tissues of peptides with structural similaritie s to angiotensin I and to bradykinin, the two best known substrates of mammalian angiotensin-converting enzyme, has not been reported. As pa rt of our study to identify potential substrates for insect angiotensi n-converting enzyme, we have investigated the susceptibility of a numb er of known insect peptide hormones and neurotransmitters to hydrolysi s by Musca domestica angiotensin-converting enzyme. Insect peptides be longing to the red pigment-concentrating hormone, leucokinin, locust t achykinin, and depolarizing peptide families were hydrolyzed by housef ly angiotensin-converting enzyme, whereas proctolin and crustacean car dioactive peptide were not substrates. Cus-DP II, LK I, LK II, and Lom -TK I were all cleaved at the penultimate C-terminal peptide bond to r elease a dipeptide amide as a major fragment with K, values of 94 +/- 11, 634 +/- 81, and 296 +/- 35 mu M for Cus-DP II, LK I, and Lom-TK I, respectively. The ability of insect angiotensin-converting enzyme to hydrolyze C-terminally amidated peptides in vitro might be of function al significance because the enzyme has been localized to neuropile reg ions of the insect brain and is present in the hemolymph of houseflies . (C) 1997 Elsevier Science Inc.