Organization of the terminal two enzymes of the heme biosynthetic pathway. Orientation of protoporphyrinogen oxidase and evidence for a membrane complex.
Organization of the terminal two enzymes of the heme biosynthetic pathway. Orientation of protoporphyrinogen oxidase and evidence for a membrane complex.
复制标题
DOI：
10.1016/s0021-9258(18)69000-3
复制
发表时间：
1988-03
期刊：
影响因子：
--
通讯作者：
Gloria Cruz FerreiraS;Tamara L. Andrew;S. W. Karr;Harry A. Daileyg
中科院分区：
文献类型：
--
作者：
Gloria Cruz FerreiraS;Tamara L. Andrew;S. W. Karr;Harry A. Daileyg
原卟啉原氧化酶 (EC 1.3.3.4) 是血红素生物合成途径的倒数第二个酶，催化从原卟啉原 IX 中去除六个氢以形成原卟啉 IX。真核生物中的酶与线粒体内膜相关。在本研究中，我们检查了这种酶溶解的要求，发现它表现为一种内在膜蛋白，只能用胆酸钠等去污剂溶解。酶相对于线粒体内膜的原位定向将活性位点置于该膜的胞质面，而不是末端途径酶亚铁螯合酶的活性位点所在的基质侧。对线粒体膜中两个末端酶的动力学的检查表明，底物通道发生在这些末端双途径酶之间。然而，对溶解的酶和膜重构酶的检查显示没有稳定复合物的证据。基于这些和之前的数据，提出了末端三途径酶的模型。
Protoporhyrinogen oxidase (EC 1.3.3.4), the penultimate enzyme of the heme biosynthetic pathway, catalyzes the removal of six hydrogens from protoporphyrinogen IX to form protoporphyrin IX. The enzyme in eukaryotes is associated with the inner mitochondrial membrane. In the present study we have examined requirements for solubilization of this enzyme and find that it behaves as an intrinsic membrane protein that is solubilized only with detergents such as sodium cholate. The in situ orientation of the enzyme with respect to the inner mitochondrial membrane places the active site on the cytosolic face of this membrane rather than the matrix side where the active site of ferrochelatase, the terminal pathway enzyme, is located. Examination of the kinetics of the two terminal enzymes in mitochondrial membranes demonstrates that substrate channeling occurs between these terminal two-pathway enzymes. However, examination of solubilized and membrane-reconstituted enzymes shows no evidence for a stable complex. Based upon these and previous data a model for the terminal three-pathway enzymes is presented.