Chepuri V, Lemieux L, Hill J, Alben J O, Gennis R B
Department of Biochemistry, University of Illinois, Urbana 61801.
Biochim Biophys Acta. 1990 Jul 25;1018(2-3):124-7. doi: 10.1016/0005-2728(90)90231-r.
The cytochrome o complex is the predominant terminal oxidase in the aerobic respiratory chain of Escherichia coli when the bacteria are grown under conditions of high aeration. The oxidase is a ubiquinol oxidase and reduces molecular oxygen to water. Electron transport through the enzyme is coupled to the generation of a protonmotive force. The purified cytochrome o complex contains four or five subunits, two protoheme IX (heme b) prosthetic groups, plus at least one Cu. The subunits are all encoded by the cyo operon. Sequence comparisons show that the cytochrome o complex is closely related to the aa3-type cytochrome c oxidase family. Gene fusions have been used to define the topology of each of the gene products. Subunits I, II, III and IV are proposed to have 15, 2, 5 and 3 transmembrane spans, respectively. The fifth gene product (cyoE) encodes a protein with 7 membrane spanning segments, and this may also be a subunit of this enzyme. Fourier transform infrared spectroscopy has been used to monitor CO bound in the active site where oxygen is reduced. These data provide definitive proof that the cytochrome o complex has a heme-copper binuclear center, similar to that present in the aa3-type cytochrome c oxidases. Site-directed mutagenesis is being utilized to define which amino acids are ligands to the heme iron and copper prosthetic groups.
细胞色素o复合体是大肠杆菌在高通气条件下生长时好氧呼吸链中的主要末端氧化酶。该氧化酶是一种泛醇氧化酶，可将分子氧还原为水。通过该酶的电子传递与质子动力势的产生相偶联。纯化的细胞色素o复合体包含四个或五个亚基、两个原血红素IX（血红素b）辅基，外加至少一个铜。这些亚基均由cyo操纵子编码。序列比较表明，细胞色素o复合体与aa3型细胞色素c氧化酶家族密切相关。基因融合已被用于确定每个基因产物的拓扑结构。亚基I、II、III和IV分别被认为具有15、2、5和3个跨膜区段。第五个基因产物（cyoE）编码一种具有7个跨膜区段的蛋白质，这也可能是该酶的一个亚基。傅里叶变换红外光谱已被用于监测结合在氧被还原的活性位点中的一氧化碳。这些数据提供了确凿的证据，证明细胞色素o复合体具有一个血红素-铜双核中心，类似于aa3型细胞色素c氧化酶中存在的中心。定点诱变正被用于确定哪些氨基酸是血红素铁和铜辅基的配体。
