Lamango N S, Nachman R J, Hayes T K, Strey A, Isaac R E
Department of Biology, University of Leeds, UK.
Peptides. 1997;18(1):47-52. doi: 10.1016/s0196-9781(96)00232-x.
The presence in insect tissues of peptides with structural similarities to angiotensin I and to bradykinin, the two best known substrates of mammalian angiotensin-converting enzyme, has not been reported. As part of our study to identify potential substrates for insect angiotensin-converting enzyme, we have investigated the susceptibility of a number of known insect peptide hormones and neurotransmitters to hydrolysis by Musca domestica angiotensin-converting enzyme. Insect peptides belonging to the red pigment-concentrating hormone, leucokinin, locust tachykinin, and depolarizing peptide families were hydrolyzed by housefly angiotensin-converting enzyme, whereas proctolin and crustacean cardioactive 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 release a dipeptide amide as a major fragment with Km values of 94 +/- 11, 634 +/- 8, and 296 +/- 35 microM 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 functional significance because the enzyme has been localized to neuropile regions of the insect brain and is present in the hemolymph of houseflies.
在昆虫组织中，尚未有关于存在与血管紧张素I和缓激肽结构相似的肽的报道，而血管紧张素I和缓激肽是哺乳动物血管紧张素转换酶最知名的两种底物。作为我们鉴定昆虫血管紧张素转换酶潜在底物研究的一部分，我们研究了多种已知昆虫肽激素和神经递质被家蝇血管紧张素转换酶水解的敏感性。属于红色素浓缩激素、亮氨酸激肽、蝗虫速激肽和去极化肽家族的昆虫肽可被家蝇血管紧张素转换酶水解，而原肌球蛋白和甲壳动物心脏活性肽则不是底物。Cus-DP II、LK I、LK II和Lom-TK I均在倒数第二个C末端肽键处裂解，释放出一种二肽酰胺作为主要片段，Cus-DP II、LK I和Lom-TK I的Km值分别为94±11、634±8和296±35μM。昆虫血管紧张素转换酶在体外水解C末端酰胺化肽的能力可能具有功能意义，因为该酶已定位在昆虫脑的神经纤维区域，并且存在于家蝇的血淋巴中。
