CO2 fixation kinetics of Halothiobacillus neapolitanus mutant carboxysomes lacking carbonic anhydrase suggest the
Zhicheng Dou1, Sabine Heinhorst, Eric B Williams
1Department of Chemistry and Biochemistry, The University of Southern Mississippi, Hattiesburg, Mississippi 39406-0001, USA.
Abstract:
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, CO(2), 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 CO(2)-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 CO(2) into and out of the carboxysome interior.
Related Concept Videos
Carbon-dioxide Fixation
The Calvin Benson Cycle
Loss of Carboxy Group as CO2: Decarboxylation of β-Ketoacids
C4 Pathway and CAM
C4 Pathway
The C4 pathway is used by plants such as...
Carbon Dioxide Transport in the Blood
Forms of CO2 Transport
1. Dissolved in plasma: A small percentage (7-10%) of CO2 is transported and dissolved directly in the plasma.
2. Carbaminohemoglobin: Just over 20% of CO2 is chemically bound to...
Loss of Carboxy Group as CO2: Decarboxylation of Malonic Acid Derivatives


