CO2 fixation kinetics of Halothiobacillus neapolitanus mutant carboxysomes lacking carbonic anhydrase suggest the shell acts as a diffusional barrier for CO2
CO2 fixation kinetics of Halothiobacillus neapolitanus mutant carboxysomes lacking carbonic anhydrase suggest the shell acts as a diffusional barrier for CO2
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DOI：
10.1074/jbc.m709285200
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发表时间：
2008-04-18
影响因子：
4.8
通讯作者：
Cannon, Gordon C.
中科院分区：
文献类型：
--
作者：
Dou, Zhicheng;Heinhorst, Sabine;Cannon, Gordon C.
被广泛接受的模型中的作用，carboxysomes的碳浓缩机制的自养细菌预测carboxysomal碳酸酐酶是一个关键的组成部分。该酶被认为是丰富的胞质碳酸氢盐，并提供核酮糖1.5-二磷酸羧化酶/加氧酶（RubisCO）与足够高浓度的其底物，CO2，以允许其有效地固定到核酮糖1，5-二磷酸内的羧基体内。在这项研究中，从野生型那不勒斯嗜盐硫杆菌和从高CO2需要的突变体，是缺乏carboxysomal碳酸酐酶纯化的carboxysomes的结构和功能进行了比较。碳固定反应的动力学常数证实了功能性carboxysomal碳酸酐酶的RubisCO有效催化的重要性。此外，在完整的和破碎的微区室和纯化的carboxysomal RubisCO的反应的比较暗示的蛋白质壳的微区室作为阻碍扩散的CO2进出的羧基内部。
The widely accepted models for the role of carboxysomes in the carbon-concentrating mechanism of autotrophic bacteria predict the carboxysomal carbonic anhydrase to be a crucial component. The enzyme is thought to dehydrate abundant cytosolic bicarbonate and provide ribulose 1.5-bisphosphate carboxylase/ oxygenase (RubisCO) sequestered within the carboxysome with sufficiently high concentrations of its substrate, CO2, to permit its efficient fixation onto ribulose 1,5-bisphosphate. In this study, structure and function of carboxysomes purified from wild type Halothiobacillus neapolitanus and from a high CO2-requiring mutant that is devoid of carboxysomal carbonic anhydrase were compared. The kinetic constants for the carbon fixation reaction confirmed the importance of a functional carboxysomal carbonic anhydrase for efficient catalysis by RubisCO. Furthermore, comparisons of the reaction in intact and broken microcompartments and by purified carboxysomal RubisCO implicated the protein shell of the microcompartment as impeding diffusion of CO2 into and out of the carboxysome interior.