Carbon Oxysulfide Is an Inhibitor of Both CO2 and HCO3 Uptake in the Cyanobacterium Synechococcus PCC7942

Abstract
Carbon oxysulfide (COS) was reinvestigated as an inhibitor of active inorganic carbon transport in cells of Synechococcus PCC7942 adapted to growth at low inorganic carbon. COS inhibited both CO2 and HCO3 transport processes in a reversible (in the short term) and mixed competitive manner. The inhibition of COS was established using both silicone oil centrifugation experiments and O2-evolution studies. The Ki for COS inhibition was 29 micromolar for CO2 transport and 110 micromolar for HCO3 transport. These results support a model of inorganic carbon transport with a central CO2 pump and an inducible HCO3 utilizing accessory protein which supplies CO2 to the primary pump.