Ethoxyzolamide Inhibition of CO2 Uptake in the Cyanobacterium Synechococcus PCC7942 without Apparent Inhibition of Internal Carbonic Anhydrase Activity 1

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RESUMO

In high inorganic carbon grown (1% CO2 [volume/volume]) cells of the cyanobacterium Synechococcus PCC7942, the carbonic anhydrase (CA) inhibitor, ethoxyzolamide (EZ), was found to inhibit the rate of CO2 uptake and to reduce the final internal inorganic carbon (Ci) pool size reached. The relationship between CO2 fixation rate and internal Ci concentration in high Ci grown cells was little affected by EZ. This suggests that in intact cells internal CA activity was unaffected by EZ. High Ci grown cells readily took up CO2 but had little or no capacity for HCO3− uptake. These cells appear to possess a CO2 utilizing Ci pump that has a CA-like function associated with the transport step such that HCO3− is the species delivered to the cell interior. This CA-like step may be the site of inhibition by EZ. Low Ci grown cells possess both CO2 uptake and HCO3− uptake activities and EZ inhibited both activities to a similar degree, suggesting that a common step in CO2 and HCO3− uptake (such as the Ci pump) may have been affected. The inhibitor had no apparent effect on internal CO2/HCO3− equilibria (internal CA function) in low Ci grown cells.

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