Department of Plant Biology, University of California, Davis, CA, 95616, USA,
Photosynth Res. 2013 Oct;116(2-3):231-4. doi: 10.1007/s11120-013-9864-8. Epub 2013 Jun 18.
This is an article on the peroxydicarbonic acid (PODCA) hypothesis of photosynthetic water oxidation, which follows our first article in this general area (Castelfranco et al., Photosynth Res 94:235-246, 2007). In this article I have expanded on the idea of a protein-bound intermediate containing inorganic carbon in some chemically bound form. PODCA is conceived in this article as constituting a bridge between two proteins of the oxygen-evolving complex (OEC) that are essential for the evolution of O2. Presumably, these are two proteins which have been shown to possess Mn-dependent carbonic anhydrase activity (Lu et al., Plant Cell Physiol 46:1944-1953, 2005; Shitov et al., Biochemistry (Moscow) 74:509-517, 2009). One of these proteins may be the D(I) of the OEC core and the other may be the PsbO extrinsic protein. I attempt to relate briefly the PODCA hypothesis to the role of two cofactors for O2 evolution: Ca(2+) and inorganic carbon. In this scheme, inorganic carbon (HCO3 (-)) mediates the oxidation of peroxide to dioxygen, thus avoiding the homolytic cleavage of the peroxide into two free radicals. I visualize the role of Ca(2+) in the binding of PODCA to two essential photosystem II proteins. I propose that PODCA alternates between two Phases. In Phase 1, PODCA is broken down with the production of O2. In Phase 2, PODCA is regenerated.
这是一篇关于过氧碳酸（PODCA）假说的光合作用水氧化的文章，该假说遵循我们在该领域的第一篇文章（Castelfranco 等人，Photosynth Res 94：235-246，2007）。在本文中，我扩展了一个想法，即蛋白质结合的中间体能以某种化学结合的形式包含无机碳。本文将 PODCA 设想为构成放氧复合物（OEC）中两种必需蛋白质之间的桥梁，这些蛋白质对于 O2 的演化至关重要。据推测，这些是两种已被证明具有 Mn 依赖性碳酸酐酶活性的蛋白质（Lu 等人，Plant Cell Physiol 46：1944-1953，2005；Shitov 等人，Biochemistry （Moscow）74：509-517，2009）。这些蛋白质之一可能是 OEC 核心的 D(I)，另一种可能是 PsbO 外在蛋白。我尝试简要地将 PODCA 假说与两个 O2 演化的辅助因子：Ca(2+)和无机碳联系起来。在这个方案中，无机碳（HCO3(-)）介导过氧化物氧化为氧气，从而避免过氧化物的均裂产生两个自由基。我将 Ca(2+)在 PODCA 与两个必需的光系统 II 蛋白结合中的作用形象化。我提出 PODCA 在两个阶段之间交替。在第一阶段，PODCA 分解产生 O2。在第二阶段，PODCA 再生。
