Biochemical Characterization Of Carboxysomes In The Cyanobacterium Synechococcus Sp.PCC7942

Abstract

Cyanobacteria possess a CO₂ concentrating mechanism (CCM) that allows cells to perform efficient CO₂ fixation. The CCM is considered to consist of two basic steps, accumulation of intracellular HCO₃^-, which is mediated by multiple active uptake systems for CO₂ and HCO₃^-, and CO₂ fixation in the Rubisco-containing micro-compartment known as carboxysome. Because of the presence of a carbonic anhydrase in the carboxysome, it is supposed that the carboxysomal carbonic anhydrase (CCA) catalyses rapid conversion of HCO₃^- to CO₂, resulting in a high local CO₂ concentration at the site of fixation. In this study, we detected high CO₂ fixation activity in partially-purified carboxysome preparations from the wild-type cells, confirming that carboxysome is the site of CO₂ fixation. By contrast, carboxysome fraction of a CCA-less mutant showed much lower CO₂ fixation activity, verifying that CCA is important for efficient CO₂ fixation.