With global warming becoming such a prevalent issue in the world, research concerning the conversion of carbon dioxide is a hot topic. Researchers have recently studied the conversion of carbon dioxide to bicarbonate in cyanobacteria. In the cells of these bacteria there are micro-compartments (carboxysomes) that contain a large amount of proteins (i.e., enzymes). Two particular proteins, rubisco and carbonic anhydrase (CA), catalyze (or induce/speed up the process) the conversion of CO2 to bicarbonate. When carbon dioxide enters the cell, the enzyme rubisco fixes the molecule to a sugar (ribulose-1,5 bisphosphate) which causes the formation of two new molecules (please see illustration below for diagram of process). Without the presence of CAs, this fixation process is tedious and much slower. However, large amounts of CAs can increase the reaction rate 1000-fold, thus yielding a much greater amount of CO2 to be fixed by rubisco. Yu and his research team conclude that this fast catalyzation is due to the fact that the process takes place in such a small area with a large concentration of proteins. Their research involved creating a nano-environment capable of entrapping large amounts of protein to induce conversion of carbon dioxide. Their results provide insight to the possibility of biomimetically converting CO2 through confining a large amount of specific proteins to a small space.
The chemical reaction for the catalyzation done by carbonic anhydrase is:
H2CO3 —(carbonic anhydrase)–> H2O+CO2
The CO2produced by this reaction is what is then converted to bicarbonate through fixation by rubisco.
Calvin Cycle: process through which rubisco aids in fixing carbon dioxide. Artist: Mike Jones.
“We report here a concept converting carbon dioxide to bicarbonate in biomimetic nanoconfiguration. Carbonic anhydrase (CA), the fastest enzyme that can covert carbon dioxide to bicarbonate, can be spontaneously entrapped in carboxylic acid group-functionalized mesoporous silica (HOOC-FMS) with super-high loading density (up to 0.5 mg of protein/mg of FMS) in sharp contrast to normal porous silica. The binding of CA to HOOC-FMS resulted in a partial conformational change comparing to the enzyme free in solution, but it can be overcome with increased protein loading density. The higher the protein loading density, the less conformational change, hence the higher enzymatic activity and the higher enzyme immobilization efficiency (up to >60%). The released enzyme still displayed the native conformational structure and the same high enzymatic activity as that prior to the enzyme entrapment, indicating that the conformational change resulted from the electrostatic interaction of CA with HOOC-FMS was not permanent. This work may provide a new approach converting carbon dioxide to bicarbonate that can be integrated with the other part of biosynthesis process for the assimilation of carbon dioxide” (Yu et al. 2011).