The substrate specificity of a purified kidney neutral endopeptidase was studied. The endopeptidase hydrolyzed a variety of biologically active peptides, such as angiotensins (angiotensins I, II and III), bradykinins (bradykinin, Lys-bradykinin, Met-Lys-bradykinin and des-9Arg-bradykinin), enkephalins (Leu-enkephalin and Met-enkephalin), neurotensin and substance P, and was found to cleave only the bonds at the amino side of hydrophobic amino acids in the peptides. However, when a hydrophobic amino acid was present at the C-terminus or at the position adjacent to the N-terminus, the bond of the hydrophobic residue was not cleaved. In further studies on the degradation of a series of homo-oligopeptides, the enzyme appeared to hydrolyze those consisting of at least a tetrapeptide unit of hydrophobic amino acids such as Ala and Phe. The specificity of the membrane-bound neutral endopeptidase from rat kidney indicated by these results can be summarized as follows : the enzyme requires at least a tetrapeptide unit for hydrolysis, and cleavage occurs only at the amino side of a hydrophobic amino acid, when one is present at the third position of the tetrapeptide unit.
纯化的肾脏中性内切肽酶的底物特异性被研究。该内切肽酶
水解多种
生物活性肽,如
血管紧张素(
血管紧张素I、II和III)、
舒缓激肽(
舒缓激肽、赖
氨酸-
舒缓激肽、甲
硫氨酸-赖
氨酸-
舒缓激肽和去-9精
氨酸-
舒缓激肽)、
脑啡肽(亮
氨酸-
脑啡肽和甲
硫氨酸-
脑啡肽)、
神经降压素和P物质,并且发现它仅在肽中疏
水氨基酸的
氨基侧切割肽键。然而,当疏
水氨基酸位于C末端或紧邻N末端的位置时,疏
水残基的肽键不会被切割。在进一步研究一系列同源寡肽的降解过程中,该酶似乎
水解那些至少由疏
水氨基酸如丙
氨酸和苯丙
氨酸组成四肽单位的肽。根据这些结果,大鼠肾脏膜结合中性内切肽酶的特异性可以总结如下:酶需要至少一个四肽单位进行
水解,并且仅在疏
水氨基酸存在于四肽单位的第三位置时,才在该疏
水氨基酸的
氨基侧进行切割。