RuBisCO (Ribulose 1,5 bisphosphate carboxylase/oxygenase) by virtue of its dual specificity towards oxygenand carbon dioxide is an important rate-limiting step in photosynthesis and is believed to be the key factor forlimited productivity of higher plants and algae. The photoautotrophic growth rate of cyanobacteria is aculmination of several factors including, rates of photosynthetic reactions, stress combating mechanisms andbasic biomass generation metabolism in combination with optimal nutrient availability, irradiance, gaseousenvironment, etc. In case of cyanobacteria, the effect of RuBisCO in affecting the multiplication rate has beenobserved to show varied response. The current paper presents the RuBisCO activity of an early divergingcyanobacterium, Gloeobacter violaceus PCC 7421 and also compares the growth rates and RuBisCO activityof various cyanobacteria. A spectrophotometric estimation in a coupled enzyme assay system of theheterologous expressed G. violaceus PCC 7421 RuBisCO in E. coli, upon purification, revealed a carboxylationactivity of LSu to be 5 nMol of phosphoglycerate min-1 mg-1 of protein, which is in coherence with theorganism’s slow growth rate. Further, the in vitro complementation of RbcL with RbcS in presence of RbcX ofG. violaceus facilitated partial reconstitution of the protein and was hence found to cause a four-foldenhancement in its specific activity. The unique characteristics of the primitive cyanobacteria, such as, absenceof thylakoids, lack of several photosystem constituting genes, slow carboxylation rate, pose limitation for itsrapid multiplication. The RuBisCO carboxylation rate is observed as not the sole but an important parameterfor obtaining optimal cell multiplication rates in photo-autotrophically multiplying cyanobacteria.
Volume 46, 2021
Continuous Article Publishing mode
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