Moser Jürgen, Bröcker Markus J
Institut für Mikrobiologie, Technische Universität Braunschweig, D-38106 Braunschweig, Germany.
Methods Mol Biol. 2011;766:129-43. doi: 10.1007/978-1-61779-194-9_9.
Nitrogenase-like dark operative protochlorophyllide oxidoreductase (DPOR) is involved in the biosynthesis of chlorophylls and bacteriochlorophylls in gymnosperms, ferns, algae, and photosynthetic bacteria. During protochlorophyllide (Pchlide) reduction, the homodimeric subunit ChlL(2) of DPOR transfers electrons on the corresponding heterotetrameric catalytic subunit (ChlN/ChlB)(2). Although DPOR shares significant amino acid sequence homology to the nitrogenase system, only the initial catalytic steps of DPOR resemble nitrogenase catalysis. Investigation of the cyanobacterial DPOR from Prochlorococcus marinus indicated that subcomplex ChlL(2) is functioning as an ATP-dependent switch protein, triggering the transient interaction of ChlL(2) and (ChlN/ChlB)(2). This dynamic subunit interplay is responsible for the transfer of a single electron from the [4Fe-4S] cluster of ChlL(2) onto a second [4Fe-4S] cluster located on (ChlN/ChlB)(2). However, the second part of DPOR catalysis is unrelated to nitrogenase catalysis, since no molybdenum-containing cofactor or a P-cluster equivalent is employed. Instead, two consecutive electron transfer steps are mediated via the [4Fe-4S] cluster of (ChlN/ChlB)(2), resulting in the reduction of the conjugated ring system of the substrate molecule Pchlide (Figs. 5.1a and 5.2).
类固氮暗操作原叶绿素酸氧化还原酶（DPOR）参与裸子植物、蕨类植物、藻类和光合细菌中叶绿素和细菌叶绿素的生物合成。在原叶绿素酸（Pchlide）还原过程中，DPOR的同型二聚体亚基ChlL(2)将电子转移到相应的异型四聚体催化亚基（ChlN/ChlB）(2)上。尽管DPOR与固氮酶系统具有显著的氨基酸序列同源性，但只有DPOR的初始催化步骤类似于固氮酶催化。对来自海洋原绿球藻的蓝细菌DPOR的研究表明，亚复合物ChlL(2)作为一种依赖ATP的开关蛋白发挥作用，触发ChlL(2)与（ChlN/ChlB）(2)的瞬时相互作用。这种动态的亚基相互作用负责将单个电子从ChlL(2)的[4Fe-4S]簇转移到位于（ChlN/ChlB）(2)上的第二个[4Fe-4S]簇上。然而，DPOR催化的第二部分与固氮酶催化无关，因为没有使用含钼辅因子或等效的P簇。相反，两个连续的电子转移步骤通过（ChlN/ChlB）(2)的[4Fe-4S]簇介导，导致底物分子Pchlide的共轭环系统还原（图5.1a和5.2）。
