EXPRESSION OF ANGIOTENSIN-CONVERTING ENZYME-RELATED CARBOXYDIPEPTIDASES IN THE LARVAE OF 4 SPECIES OF FLY

HieACE, a soluble 70 kDa protein related to the angiotensin-converting enzyme (ACE) has recently been identified, characterized and cloned f rom the adult buffalo fly (Haematobia irritans exigua), HieACE is enzy matically similar to the mammalian ACEs and its predicted amino acid s equence has 42% identity with the mammalian testicular ACE, In adult H .i. exigua, HieACE expression is restricted to the compound ganglion a nd posterior midgut, and the maturing male reproductive system, Wester n blot analysis was used to investigate the expression of HieACE and i ts homologues in the larvae of H.i. exigua, Drosophila melanogaster, t he sheep blowfly (Lucilia cuprina), the Old World screwworm fly (Chrys omya bezziana) and a secondary strike fly, Chrysomya rufifacies. Dipte ran ACE homologues of 65-70 kDa were detected in all the larval instar s investigated, Most of the immunoreactive proteins were concentrated in the soluble fraction, The first and second larval instars of L. cup rina and C. bezziana appeared to express two ACE homologues, These lar vae were also found to secrete (or excrete) the ACE homologue in larva l cultures, The presence of ACE-like enzymes in these larvae was confi rmed by the measurement of carboxydipeptidase activity that was inhibi ted by the specific ACE inhibitor, captopril, The tissue distributions of the ACE homologues in the third instar larvae of H.i. exigua and L . cuprina were examined, As in adult H.i. exigua, HieACE was detected in the larval ganglion, but in contrast to the restricted distribution in the adult stage midgut, HieACE was found throughout the digestive system, and in the salivary glands of H.i. exigua larvae. The expressi on pattern in the gut of L. cuprina larvae was similar despite the dif ferences in diet and habitat, The most striking difference from the ad ult stage H.i. exigua was the expression of HieACE and its L. cuprina homologues in the hindgut and Malpighian tubules of these larvae, Thes e results suggest that the role(s) played by the dipteran ACE-like enz ymes differ between the adult and larval stages. (C) 1997 Elsevier Sci ence Ltd.