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对聚球藻属蓝细菌细长聚球藻的羧基体β型碳酸酐酶在1,5-二磷酸核酮糖羧化作用中所起作用的体外和体内分析。

In vitro and in vivo analyses of the role of the carboxysomal β-type carbonic anhydrase of the cyanobacterium Synechococcus elongatus in carboxylation of ribulose-1,5-bisphosphate.

作者信息

Nishimura Takashi, Yamaguchi Osamu, Takatani Nobuyuki, Maeda Shin-Ichi, Omata Tatsuo

机构信息

Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601, Japan.

出版信息

Photosynth Res. 2014 Sep;121(2-3):151-7. doi: 10.1007/s11120-014-9986-7. Epub 2014 Mar 2.

Abstract

The carboxylase activities of crude carboxysome preparations obtained from the wild-type Synechococcus elongatus strain PCC 7942 strain and the mutant defective in the carboxysomal carbonic anhydrase (CA) were compared. The carboxylation reaction required high concentrations of bicarbonate and was not even saturated at 50 mM bicarbonate. With the initial concentrations of 50 mM and 25 mM for bicarbonate and ribulose-1,5-bisphosphate (RuBP), respectively, the initial rate of RuBP carboxylation by the mutant carboxysome (0.22 μmol mg(-1) protein min(-1)) was only 30 % of that observed for the wild-type carboxysomes (0.71 μmol mg(-1) protein min(-1)), indicating the importance of the presence of CA in efficient catalysis by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). While the mutant defective in the ccmLMNO genes, which lacks the carboxysome structure, could grow under aeration with 2 % (v/v) CO2 in air, the mutant defective in ccaA as well as ccmLMNO required 5 % (v/v) CO2 for growth, indicating that the cytoplasmically localized CcaA helped utilization of CO2 by the cytoplasmically localized Rubisco by counteracting the action of the CO2 hydration mechanism. The results predict that overexpression of Rubisco would hardly enhance CO2 fixation by the cyanobacterium at CO2 levels lower than 5 %, unless Rubisco is properly organized into carboxysomes.

摘要

比较了从野生型聚球藻属细长杆菌菌株PCC 7942和羧基体碳酸酐酶(CA)缺陷型突变体中获得的粗羧基体制剂的羧化酶活性。羧化反应需要高浓度的碳酸氢盐,即使在50 mM碳酸氢盐时也未达到饱和。分别以50 mM和25 mM的初始浓度加入碳酸氢盐和1,5-二磷酸核酮糖(RuBP),突变体羧基体对RuBP的羧化初始速率(0.22 μmol mg⁻¹蛋白质 min⁻¹)仅为野生型羧基体(0.71 μmol mg⁻¹蛋白质 min⁻¹)的30%,这表明CA的存在对于1,5-二磷酸核酮糖羧化酶/加氧酶(Rubisco)的高效催化至关重要。虽然缺乏羧基体结构的ccmLMNO基因缺陷型突变体在含2%(v/v)CO₂的空气中通气培养时能够生长,但ccaA以及ccmLMNO基因缺陷型突变体生长需要5%(v/v)的CO₂,这表明定位于细胞质的CcaA通过抵消CO₂水合机制的作用,帮助定位于细胞质的Rubisco利用CO₂。结果预测,除非Rubisco正确组装到羧基体中,否则在CO₂水平低于5%时,Rubisco的过表达几乎不会增强蓝细菌对CO₂的固定。

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