Carbon Acquisition Mechanisms of Algae: Carbon Dioxide Diffusion and Carbon Dioxide Concentrating Mechanisms
Carbon Acquisition Mechanisms of Algae: Carbon Dioxide Diffusion and Carbon Dioxide Concentrating Mechanisms
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DOI：
10.1007/978-94-007-1038-2_11
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
J. Raven;J. Beardall
中科院分区：
文献类型：
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作者：
J. Raven;J. Beardall
蓝藻和藻类中至少95%的有机碳被Rubisco固定为CO2。Rubisco的动力学性质使得即使具有最高CO2：O2选择性的遗传变体也将显示有限的CO2固定和显著的加氧酶活性，如果CO2和O2流入细胞仅由扩散驱动。这是尤其是情况下，与低气体扩散系数相对于扩散边界层厚度的沉水藻类。有证据表明，从气体交换性能和细胞内无机浓度无机碳浓缩机制（CCM）的功能，在所有的蓝藻和许多藻类。从理论上讲，集束弹药可通过三类机制运作：第一种机制是HCO 2和/或CO2主动跨膜转运，第二种机制是通过类似于C4和CAM的生化机制泵送CO2（景天科酸代谢）途径，第三种机制涉及H+的主动运输，产生供应HCO 2的酸室，这产生了高的（平衡）CO2浓度，将CO2供应给附近碱性更强的隔室中的Rubisco。大多数证据支持第一种机制，认为它是藻类中CCM活性的原因。膜的CO2（和HCO 2）渗透性在确定无机C从CCM渗漏的程度以及从培养基向Rubisco扩散CO2供应的功能方面是至关重要的。像碳酸酐酶一样，CCM可能是多系的。
At least 95% ofthe organic carbon in cyanobacteria and algae has been fixed as CO2by Rubisco. The kinetic properties of Rubisco are such that even the genetic variants with the highest CO2: 02selectivity would show limited CO2fixation and significant oxygenase activity if CO2and 02 fluxes into cells are driven solely by diffusion. This is especiallythe case for submerged algae with lowgas diffusion coefficients relative to diffusion boundary layer thicknesses. There is evidence from gas exchange properties and intracellular inorganic concentration that inorganic carbon concentrating mechanisms (CCMs) function in all cyanobacteria and many algae. CCMs can, in theory, operate through three categories of mechanism: the first mechanism is active transport of HCOj and/or CO2across membranes, the second is CO2pumping by a biochemical mechanism analogous to C4 and CAM (Crassulacean Acid Metabolism) pathways in higher land plants, and the third mechanism involves active transport of H+ producing an acid compartment supplied with HCOj, which generates a high (equilibrium) CO2concentration that supplies CO2to Rubisco in a nearby more alkaline compartment. Most evidence favors the first mechanism as being responsible for CCM activity in algae. The CO2 (and HCOj) permeability of membranes is crucial in defining the extent of inorganic C leakage from CCMs, and the functioning ofdiffusive CO2supply to Rubisco from the medium. Like carbonic anhydrases, CCMs, are probably polyphyletic.