Ferreira G C, Andrew T L, Karr S W, Dailey H A
Department of Microbiology, University of Georgia, Athens 30602.
J Biol Chem. 1988 Mar 15;263(8):3835-9.
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.
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去除六个氢以形成原卟啉IX。真核生物中的该酶与线粒体内膜相关。在本研究中，我们研究了该酶溶解的条件，发现它表现为一种内在膜蛋白，仅用胆酸钠等去污剂才能溶解。该酶相对于线粒体内膜的原位取向使活性位点位于该膜的胞质面，而不是位于末端途径酶铁螯合酶活性位点所在的基质侧。对线粒体膜中两种末端酶的动力学研究表明，这两种末端途径酶之间发生底物通道化。然而，对溶解和膜重构酶的研究没有显示出稳定复合物的证据。基于这些和以前的数据，提出了一个关于末端三途径酶的模型。
