Center for Biophysics and Quantitative Biology, University of Illinois , Urbana, Illinois 61801, United States.
Department of Biochemistry, University of Illinois , Urbana, Illinois 61801, United States.
J Am Chem Soc. 2017 Jun 21;139(24):8346-8354. doi: 10.1021/jacs.7b03883. Epub 2017 Jun 6.
Cytochrome bo is a respiratory proton-pumping oxygen reductase that is a member of the heme-copper superfamily that utilizes ubiquinol-8 (QH) as a substrate. The current consensus model has QH oxidized at a low affinity site (Q), passing electrons to a tightly bound quinone cofactor at a high affinity site (Q site) that stabilizes the one-electron reduced ubisemiquinone, facilitating the transfer of electrons to the redox active metal centers where O is reduced to water. The current work shows that the Q bound to the Q site is more dynamic than previously thought. In addition, mutations of residues at the Q site that do not abolish activity have been re-examined and shown to have properties expected of mutations at the substrate binding site (Q): an increase in the K of the substrate ubiquinol-1 (up to 4-fold) and an increase in the apparent K of the inhibitor HQNO (up to 8-fold). The data suggest that there is only one binding site for ubiquinol in cyt bo and that site corresponds to the Q site.
细胞色素 bo 是一种呼吸质子泵氧还原酶，属于血红素铜超级家族的成员，利用泛醌-8（QH）作为底物。目前的共识模型认为 QH 在低亲和力位点（Q）被氧化，电子传递给高亲和力位点（Q 位点）上紧密结合的醌辅因子，该辅因子稳定单电子还原的 ubiisemiquinone，促进电子向氧化还原活性金属中心转移，在那里 O 被还原为水。目前的工作表明，与 Q 位点结合的 Q 比以前认为的更具动态性。此外，对 Q 位点残基的突变（不会破坏活性）进行了重新检查，结果表明这些突变具有在底物结合位点（Q）处突变的特性：底物泛醇-1（高达 4 倍）的 K 增加，以及抑制剂 HQNO（高达 8 倍）的表观 K 增加。数据表明，细胞色素 bo 中只有一个泛醇结合位点，该位点对应于 Q 位点。
