Most CO2 on Earth is fixed into organic matter via reactions catalysed by enzymes called carboxylases. CO2-fixation via carboxylases occurs in the Calvin-Benson-Bassham (CBB) cycle, and the crucial role in this cycle is played by RubisCO (D-ribulose 1,5-bisphosphate carboxylase/oxygenase). CO2 can also be fixed by pathways, where a reduction of CO2 to formate or carbon monoxide (CO) occurs. The latter reactions are performed by so-called CO2-reductases e.g. formate dehydrogenase (FDH), carbon-monooxide (CO) dehydrogenase (CODH), and crotonyl-CoA reductase/carboxylase (CCR). In general, a simple model of enzymatic activity based only on a turnover rate of an enzyme for an appropriate substrate (kcat) is insufficient. Based on estimated metabolic costs of each amino acid, the average energetic costs of amino acid biosynthesis (Eaa), and the total costs (ET) for selected CO2-fixing enzymes were analyzed concerning 1) kcat for CO2 (kC), and 2) specificity factor (Srel) for RubisCO. A comparison of Eaa and ET to their kC showed that CODH and FDHs do not need to be more efficient enzymes in CO2 capturing pathways than some forms of RubisCO. CCR was the only both low-cost and highly active CO2-fixing enzyme. The obtained results showed also that there exists an evolutionarily conserved trade-off between Srel of RubisCOs and the energetic demands needed for their biosynthesis. Phylogenetic analysis demonstrated that RubisCO, CODH, FDH, and CCR are enzymes formed as a result of parallel evolution. Moreover, the kinetic parameters (kC) of CO2-fixing enzymes were plausibly optimized already at the early stages of life evolution on Earth.

中文翻译：

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RubisCO 的活性及其生物合成的能量需求。与 CO2 还原酶的比较研究

地球上的大多数二氧化碳通过称为羧化酶的酶催化的反应固定在有机物质中。通过羧化酶固定 CO2 发生在 Calvin-Benson-Bassham (CBB) 循环中，RubisCO（D-核酮糖 1,5-二磷酸羧化酶/加氧酶）在该循环中发挥关键作用。CO2 也可以通过途径固定，其中 CO2 还原为甲酸盐或一氧化碳 (CO)。后一反应由所谓的 CO2 还原酶进行，例如甲酸脱氢酶 (FDH)、一氧化碳 (CO) 脱氢酶 (CODH) 和巴豆酰辅酶 A 还原酶/羧化酶 (CCR)。通常，仅基于酶对适当底物 (kcat) 的周转率的酶活性的简单模型是不够的。基于每种氨基酸的估计代谢成本，氨基酸生物合成的平均能量成本 (Eaa)，并对选定的 CO2 固定酶的总成本 (ET) 进行了分析，涉及 1) CO2 的 kcat (kC)，和 2) RubisCO 的特异性因子 (Srel)。Eaa 和 ET 与其 kC 的比较表明，在 CO2 捕获途径中，CODH 和 FDH 不需要是比某些形式的 RubisCO 更有效的酶。CCR 是唯一既低成本又高活性的 CO2 固定酶。获得的结果还表明，RubisCOs 的 Srel 与其生物合成所需的能量需求之间存在进化上保守的权衡。系统发育分析表明，RubisCO、CODH、FDH 和 CCR 是平行进化的结果。此外，在地球生命进化的早期阶段，CO2 固定酶的动力学参数 (kC) 似乎已经得到优化。