Dismukes G C, Klimov V V, Baranov S V, Kozlov Y N, DasGupta J, Tyryshkin A
Department of Chemistry, Hoyt Laboratory, Princeton University, Princeton, NJ 08544, USA.
Proc Natl Acad Sci U S A. 2001 Feb 27;98(5):2170-5. doi: 10.1073/pnas.061514798.
The evolution of O(2)-producing cyanobacteria that use water as terminal reductant transformed Earth's atmosphere to one suitable for the evolution of aerobic metabolism and complex life. The innovation of water oxidation freed photosynthesis to invade new environments and visibly changed the face of the Earth. We offer a new hypothesis for how this process evolved, which identifies two critical roles for carbon dioxide in the Archean period. First, we present a thermodynamic analysis showing that bicarbonate (formed by dissolution of CO(2)) is a more efficient alternative substrate than water for O(2) production by oxygenic phototrophs. This analysis clarifies the origin of the long debated "bicarbonate effect" on photosynthetic O(2) production. We propose that bicarbonate was the thermodynamically preferred reductant before water in the evolution of oxygenic photosynthesis. Second, we have examined the speciation of manganese(II) and bicarbonate in water, and find that they form Mn-bicarbonate clusters as the major species under conditions that model the chemistry of the Archean sea. These clusters have been found to be highly efficient precursors for the assembly of the tetramanganese-oxide core of the water-oxidizing enzyme during biogenesis. We show that these clusters can be oxidized at electrochemical potentials that are accessible to anoxygenic phototrophs and thus the most likely building blocks for assembly of the first O(2) evolving photoreaction center, most likely originating from green nonsulfur bacteria before the evolution of cyanobacteria.
利用水作为末端还原剂产生氧气的蓝细菌的进化，将地球大气转变为适合有氧代谢和复杂生命进化的环境。水氧化的创新使光合作用能够侵入新环境，并显著改变了地球的面貌。我们为这一过程的进化提出了一个新假说，该假说确定了太古宙时期二氧化碳的两个关键作用。首先，我们进行了一项热力学分析，结果表明，碳酸氢盐（由二氧化碳溶解形成）是产氧光合生物产生氧气比水更有效的替代底物。这一分析阐明了长期以来关于光合作用产氧的“碳酸氢盐效应”的起源。我们提出，在产氧光合作用的进化过程中，碳酸氢盐在水之前是热力学上更优的还原剂。其次，我们研究了水中锰（II）和碳酸氢盐的形态，发现在模拟太古宙海洋化学的条件下，它们形成了锰-碳酸氢盐簇作为主要形态。这些簇已被发现是生物合成过程中组装水氧化酶四氧化锰核心的高效前体。我们表明，这些簇可以在无氧光合生物可达到的电化学电位下被氧化，因此是组装第一个产生氧气的光反应中心最可能的构建块，很可能起源于蓝细菌进化之前的绿色非硫细菌。
