Bond J S, Butler P E, Beynon R J
Biomed Biochim Acta. 1986;45(11-12):1515-21.
Two metalloendopeptidases, meprin and endopeptidase-24.11 ("24.11"), were isolated from mouse kidney membranes, and their structural and catalytic properties were investigated. The enzymes both cross-react with antibodies prepared in rabbits against purified preparations of meprin; thus they share some immunologic determinants. Meprin and 24.11 have similar subunit molecular weights of 85 000 and 90 000, respectively, as demonstrated after sodium dodecyl sulfate polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol. However, under non-reducing conditions, meprin migrates as an oligomer while 24.11 remains monomeric. This and other data indicate that meprin subunits are linked by disulfide bridges, whereas endopeptidase-24.11 subunits are not covalently linked. Both endopeptidases hydrolyze insulin B chain and are totally inhibited by EDTA and o-phenanthroline. The activity of 24.11 against insulin B chain was totally inhibited by low concentrations of phosphoramidon (less than 2 nM), whereas meprin was not inhibited by concentrations of this inhibitor as high as 20 microM. Large proteins are not substrates for endopeptidase-24.11, while meprin degrades proteins such as azocasein rapidly (apparent Km = 0.65 mg/ml). Meprin appears to require an extended polypeptide chain in substrates while 24.11 prefers smaller peptides as substrates. Both endopeptidases have a preference for peptide bonds that contain hydrophobic amino acids. With the octapeptide angiotensin II as substrate, both enzymes hydrolyze the central Tyr-Ile bond; 24.11 also cleaves at Arg-Val and Ile-His. The two endopeptidases show many similarities immunologically, structurally and catalytically, however, they display distinct characteristics which may be physiologically important.
从鼠肾膜中分离出两种金属内肽酶，即膜型金属内肽酶（meprin）和内肽酶 - 24.11（“24.11”），并对它们的结构和催化特性进行了研究。这两种酶都能与用兔制备的针对纯化的膜型金属内肽酶制剂的抗体发生交叉反应；因此它们具有一些共同的免疫决定簇。经在2 - 巯基乙醇存在下进行十二烷基硫酸钠聚丙烯酰胺凝胶电泳后显示，膜型金属内肽酶和24.11的亚基分子量分别相似，为85000和90000。然而，在非还原条件下，膜型金属内肽酶以寡聚体形式迁移，而24.11则保持单体形式。这一现象及其他数据表明，膜型金属内肽酶亚基通过二硫键相连，而内肽酶 - 24.11亚基并非共价连接。两种内肽酶均能水解胰岛素B链，且完全受乙二胺四乙酸（EDTA）和邻菲啰啉抑制。低浓度的磷酰胺素（小于2 nM）就能完全抑制24.11对胰岛素B链的活性，而膜型金属内肽酶在高达20 μM的该抑制剂浓度下仍未受抑制。大分子蛋白质不是内肽酶 - 24.11的底物，而膜型金属内肽酶能快速降解诸如偶氮酪蛋白等蛋白质（表观Km = 0.65 mg/ml）。膜型金属内肽酶似乎需要底物中有延伸的多肽链，而24.11则更倾向于以较小的肽作为底物。两种内肽酶都偏好含有疏水氨基酸的肽键。以八肽血管紧张素II为底物时，两种酶都能水解中间的Tyr - Ile键；24.11还能在Arg - Val和Ile - His处切割。这两种内肽酶在免疫、结构和催化方面有许多相似之处，然而，它们也表现出一些可能具有生理重要性的独特特征。
