The ins and outs of CO2.
The ins and outs of CO2.
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DOI：
10.1093/jxb/erv451
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发表时间：
2016-01
影响因子：
6.9
通讯作者：
Beardall J
中科院分区：
文献类型：
--
作者：
Raven JA;Beardall J
提供给Rubisco的CO2可能涉及扩散的CO2助熔剂或CO2浓缩机制。这两种机制分别涉及光呼吸和泄漏造成的二氧化碳损失。无机C在光合作用组织中的内流和外流难以区分；这篇文章检查了什么是已知的，哪里有知识空白。不可逆脱羧酶产生二氧化碳，而二氧化碳是作为羧化酶和脱羧酶的酶的底物/产物。一些不可逆羧化酶使用二氧化碳；另一些则使用HCO3 -。脂质双分子层的渗透与二氧化碳选择性膜蛋白在下坡、无能量的二氧化碳运动中的相对作用尚不清楚。被动渗透解释了大多数CO2的进入，包括具有C3生理和生物化学的陆生和水生生物，陆生C4植物和所有的天冬氨酸代谢（CAM）植物，以及HCO3 -在CO2浓缩机制（CCM）功能中使用的一些机制的一部分，尽管在某些情况下需要进一步的工作来测试其机制。然而，有一些证据表明藻类的质膜上有活跃的二氧化碳流入。在所有蓝藻和一些藻类的CCMs中，质膜上的HCO3活跃内流是基础。HCO3 -也可以进入一些藻类叶绿体，可能作为CCM的一部分。CCMs导致的细胞内高CO2和HCO3 -池导致涉及CO2的泄漏，偶尔也会导致HCO3 -泄漏。蓝藻和微藻CCM的泄漏涉及进入CCM的总无机C的一半，但有时更多；在大多数环境中，陆生C4植物的泄漏量较低。对于其他具有CCMs的生物的泄漏知之甚少，尽管考虑到泄漏得到了更好的检查，泄漏发生并增加了净碳同化的能量成本。
CO2 supply to Rubisco can involve diffusive CO2 fluxes or a CO2 concentrating mechanism. The mechanisms involve CO2 loss in photorespiration or by leakage, respectively. It is difficult to distinguish influx and efflux of inorganic C in photosynthesizing tissues; this article examines what is known and where there are gaps in knowledge. Irreversible decarboxylases produce CO2, and CO2 is the substrate/product of enzymes that act as carboxylases and decarboxylases. Some irreversible carboxylases use CO2; others use HCO3 –. The relative role of permeation through the lipid bilayer versus movement through CO2-selective membrane proteins in the downhill, non-energized, movement of CO2 is not clear. Passive permeation explains most CO2 entry, including terrestrial and aquatic organisms with C3 physiology and biochemistry, terrestrial C4 plants and all crassulacean acid metabolism (CAM) plants, as well as being part of some mechanisms of HCO3 – use in CO2 concentrating mechanism (CCM) function, although further work is needed to test the mechanism in some cases. However, there is some evidence of active CO2 influx at the plasmalemma of algae. HCO3 – active influx at the plasmalemma underlies all cyanobacterial and some algal CCMs. HCO3 – can also enter some algal chloroplasts, probably as part of a CCM. The high intracellular CO2 and HCO3 – pools consequent upon CCMs result in leakage involving CO2, and occasionally HCO3 –. Leakage from cyanobacterial and microalgal CCMs involves up to half, but sometimes more, of the gross inorganic C entering in the CCM; leakage from terrestrial C4 plants is lower in most environments. Little is known of leakage from other organisms with CCMs, though given the leakage better-examined organisms, leakage occurs and increases the energetic cost of net carbon assimilation.