Borisov Vitaliy B, Gennis Robert B, Hemp James, Verkhovsky Michael I
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991, Russian Federation.
Biochim Biophys Acta. 2011 Nov;1807(11):1398-413. doi: 10.1016/j.bbabio.2011.06.016. Epub 2011 Jul 1.
Cytochrome bd is a respiratory quinol: O₂ oxidoreductase found in many prokaryotes, including a number of pathogens. The main bioenergetic function of the enzyme is the production of a proton motive force by the vectorial charge transfer of protons. The sequences of cytochromes bd are not homologous to those of the other respiratory oxygen reductases, i.e., the heme-copper oxygen reductases or alternative oxidases (AOX). Generally, cytochromes bd are noteworthy for their high affinity for O₂ and resistance to inhibition by cyanide. In E. coli, for example, cytochrome bd (specifically, cytochrome bd-I) is expressed under O₂-limited conditions. Among the members of the bd-family are the so-called cyanide-insensitive quinol oxidases (CIO) which often have a low content of the eponymous heme d but, instead, have heme b in place of heme d in at least a majority of the enzyme population. However, at this point, no sequence motif has been identified to distinguish cytochrome bd (with a stoichiometric complement of heme d) from an enzyme designated as CIO. Members of the bd-family can be subdivided into those which contain either a long or a short hydrophilic connection between transmembrane helices 6 and 7 in subunit I, designated as the Q-loop. However, it is not clear whether there is a functional consequence of this difference. This review summarizes current knowledge on the physiological functions, genetics, structural and catalytic properties of cytochromes bd. Included in this review are descriptions of the intermediates of the catalytic cycle, the proposed site for the reduction of O₂, evidence for a proton channel connecting this active site to the bacterial cytoplasm, and the molecular mechanism by which a membrane potential is generated.
细胞色素bd是一种呼吸醌：O₂氧化还原酶，存在于许多原核生物中，包括一些病原体。该酶的主要生物能量功能是通过质子的矢量电荷转移产生质子动力。细胞色素bd的序列与其他呼吸氧还原酶，即血红素-铜氧还原酶或交替氧化酶（AOX）的序列不同源。一般来说，细胞色素bd因其对O₂的高亲和力和对氰化物抑制的抗性而值得关注。例如，在大肠杆菌中，细胞色素bd（具体为细胞色素bd-I）在O₂限制条件下表达。bd家族的成员包括所谓的氰化物不敏感醌氧化酶（CIO），它们通常血红素d的含量较低，但在至少大多数酶群体中，用血红素b代替了血红素d。然而，目前尚未确定区分具有化学计量血红素d的细胞色素bd与被指定为CIO的酶的序列基序。bd家族的成员可细分为在亚基I的跨膜螺旋6和7之间含有长或短亲水性连接的成员，该连接称为Q环。然而，尚不清楚这种差异是否具有功能后果。本综述总结了关于细胞色素bd的生理功能、遗传学、结构和催化特性的当前知识。本综述包括催化循环中间体的描述、O₂还原的提议位点、连接该活性位点与细菌细胞质的质子通道的证据以及产生膜电位的分子机制。
