von Ballmoos Christoph, Adelroth Pia, Gennis Robert B, Brzezinski Peter
Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
Biochim Biophys Acta. 2012 Apr;1817(4):650-7. doi: 10.1016/j.bbabio.2011.11.015. Epub 2011 Dec 7.
The respiratory heme-copper oxidases catalyze reduction of O(2) to H(2)O, linking this process to transmembrane proton pumping. These oxidases have been classified according to the architecture, location and number of proton pathways. Most structural and functional studies to date have been performed on the A-class oxidases, which includes those that are found in the inner mitochondrial membrane and bacteria such as Rhodobacter sphaeroides and Paracoccus denitrificans (aa(3)-type oxidases in these bacteria). These oxidases pump protons with a stoichiometry of one proton per electron transferred to the catalytic site. The bacterial A-class oxidases use two proton pathways (denoted by letters D and K, respectively), for the transfer of protons to the catalytic site, and protons that are pumped across the membrane. The B-type oxidases such as, for example, the ba(3) oxidase from Thermus thermophilus, pump protons with a lower stoichiometry of 0.5 H(+)/electron and use only one proton pathway for the transfer of all protons. This pathway overlaps in space with the K pathway in the A class oxidases without showing any sequence homology though. Here, we review the functional properties of the A- and the B-class ba(3) oxidases with a focus on mechanisms of proton transfer and pumping.
呼吸血红素-铜氧化酶催化将O₂还原为H₂O，并将此过程与跨膜质子泵浦相联系。这些氧化酶已根据质子途径的结构、位置和数量进行了分类。迄今为止，大多数结构和功能研究都是针对A类氧化酶进行的，其中包括线粒体内膜以及诸如球形红杆菌和反硝化副球菌等细菌（这些细菌中的aa₃型氧化酶）中发现的氧化酶。这些氧化酶以每转移一个电子到催化位点泵出一个质子的化学计量比来泵浦质子。细菌A类氧化酶使用两条质子途径（分别用字母D和K表示），用于将质子转移到催化位点以及跨膜泵出的质子。B型氧化酶，例如嗜热栖热菌的ba₃氧化酶，以较低的化学计量比0.5 H⁺/电子泵浦质子，并且仅使用一条质子途径来转移所有质子。尽管该途径在空间上与A类氧化酶中的K途径重叠，但未显示出任何序列同源性。在此，我们综述A类和B类ba₃氧化酶的功能特性，重点关注质子转移和泵浦机制。
