Turner A J, Hryszko J, Hooper N M, Dowdall M J
J Neurochem. 1987 Mar;48(3):910-6. doi: 10.1111/j.1471-4159.1987.tb05603.x.
The electric organ of Torpedo marmorata contains a membrane-bound, captopril-sensitive metallopeptidase that resembles mammalian angiotensin converting enzyme (peptidyl dipeptidase A; EC 3.4.15.1). The Torpedo enzyme has now been purified to apparent homogeneity from electric organ by a procedure involving affinity chromatography using the selective inhibitor lisinopril immobilised to Sepharose via a 28-A spacer arm. The purified protein, like the mammalian enzyme, acted as a peptidyl dipeptidase in cleaving dipeptides from the C-terminus of a variety of peptide substrates, including angiotensin I, bradykinin, [Met5]enkephalin, [Leu5]enkephalin, and the model substrate hippuryl (benzoylglycyl; BzGly)-His-Leu. The hydrolysis of BzGly-His-Leu was activated by Cl-. Enzyme activity was inhibited by classical angiotensin converting enzyme inhibitors, including captopril, enalaprilat (MK422), and lisinopril (MK521). Torpedo angiotensin converting enzyme, like its mammalian counterpart, was also able to act as an endopeptidase in hydrolysing the amidated neuropeptide substance P. Hydrolysis of substance P occurred primarily at the Phe8-Gly9 bond with release of the C-terminal tripeptide, Gly-Leu-MetNH2, and this hydrolysis was blocked by selective inhibitors. The Torpedo enzyme was recognised by a polyclonal antibody to pig kidney angiotensin converting enzyme on immunoelectrophoretic (Western) blot analysis. Thus, on the basis of substrate specificity, inhibitor sensitivity, and immunological criteria, the Torpedo enzyme closely resembles mammalian angiotensin converting enzyme. However, the Torpedo enzyme appears somewhat larger (Mr = 190,000) than the pig kidney enzyme (Mr = 180,000) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The endogenous peptide substrate(s) for Torpedo electric organ angiotensin converting enzyme and the physiological role of the enzyme in this tissue remain to be evaluated.
电鳐（Torpedo marmorata）的电器官含有一种膜结合的、对卡托普利敏感的金属肽酶，它类似于哺乳动物的血管紧张素转换酶（肽基二肽酶A；EC 3.4.15.1）。现在，通过一种涉及亲和层析的方法，用电鳐的电器官将这种酶纯化至表观均一，该方法使用通过28 Å间隔臂固定在琼脂糖凝胶上的选择性抑制剂赖诺普利。纯化后的蛋白质与哺乳动物的酶一样，在从多种肽底物的C末端切割二肽时表现为肽基二肽酶，这些底物包括血管紧张素I、缓激肽、[Met5]脑啡肽、[Leu5]脑啡肽以及模型底物马尿酸（苯甲酰甘氨酰；BzGly）-His-Leu。BzGly-His-Leu的水解被Cl-激活。酶活性被经典的血管紧张素转换酶抑制剂抑制，包括卡托普利、依那普利拉（MK422）和赖诺普利（MK521）。电鳐血管紧张素转换酶与其哺乳动物对应物一样，也能够作为一种内肽酶水解酰胺化的神经肽P物质。P物质的水解主要发生在Phe8-Gly9键处，释放出C末端三肽Gly-Leu-MetNH2，并且这种水解被选择性抑制剂阻断。在免疫电泳（Western）印迹分析中，电鳐的酶被抗猪肾血管紧张素转换酶的多克隆抗体识别。因此，基于底物特异性、抑制剂敏感性和免疫学标准，电鳐的酶与哺乳动物的血管紧张素转换酶非常相似。然而，在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳上，电鳐的酶似乎比猪肾酶（Mr = 180,000）稍大（Mr = 190,000）。电鳐电器官血管紧张素转换酶的内源性肽底物以及该酶在该组织中的生理作用仍有待评估。
