Active Rubisco is the proportion of enzyme that is catalytically competent and can contribute to the process of CO2 fixation by carboxylation (Carfts-Brandner and Salvucci 2000). For Rubisco to remain activated, it requires the ATPase Rubisco activator enzyme known as RCA to facilitate the removal of sugar phosphates from the active site. In the absence of a molecular 3D structure of RCA, understanding the precise interaction details between RCA and Rubisco remains obscure. Until the 3D structure details are available, researchers deal with RCA as an ATPase from AAA+ protein family (Neuwald et al. 1999). This protein family members are known to use a region close to the C-terminal domain ...view middle of the document...
2007). Therefore, RCA is a major limiting factor for the process of CO2 fixation leaded by Rubisco and requires more attention when planning for enhancing CO2 fixation or the photosynthesis as a whole.
Mutagenesis studies have always used microbial systems as a tool for screening functional Rubisco or RCA through positive selection or complementation of auxotrophic mutants (Spreitzer et al. 2001; Smith and Tabita 2003), these evolutionary studies were designed to use the chemoautotrophic or photosynthetic microorganisms that already possess the Rubisco-like proteins and the CO2 fixation process within their genomes (Parikh et al. 2006). The outcome kinetics of such studies were largely affected by the internal proteins of the CO2 fixing microorganism with results that expressed the novel functional Rubisco along with the other existing mechanisms that phototrophic cells use in fixing CO2 (Parikh et al. 2006). Recently, researchers are redirecting their research to use E. coli that has been metabolically engineered in their screening tests (Mueller-Cajar and Whitney 2008). Metabolically engineered E. coli offers a perfect screening system for functional Rubisco mutants, E. coli does not fix CO2 but it possess 8 of 11 Calvin Cycle enzymes and it is relatively easy to engineer (Parikh et al. 2006). The advantages C. coli presents over the other microorganisms as a tool for functional Rubisco screening...
