Driving Forces for Bicarbonate Transport in the Cyanobacterium Synechococcus R-2 (PCC 7942).
AUTOR(ES)
Ritchie, R. J.
RESUMO
Air-grown Synechococcus R-2 (PCC 7942) cultures grown in BG-11 medium are very alkaline (outside pH is 10.0) and use HCO3- as their inorganic carbon source. The cells showed a dependence on Na+ for photosynthesis, but low Na+ conditions (1 mol m-3) were sufficient to support saturating photosynthesis. The intracellular dissolved inorganic carbon in the light was greater than 20 mol m-3 in both low-Na+ conditions and in BG-11 medium containing the usual [Na+] (24 mol m-3, designated high-Na+ conditions). The electrochemical potential for HCO3- in the light was in excess of 25 kJ mol-1, even in high-Na+ conditions. The Na+-motive force was greater than -12 kJ mol-1 under both Na+ conditions. On thermodynamic grounds, an Na+-driven co-port process would need to have a stoichiometry of 2 or greater ([greater than or equal to]2Na+ in/HCO3-1 in), but we show that Na+ or K+ fluxes cannot be linked to HCO3- transport. Na+ and K+ fluxes were unaffected by the presence or absence of dissolved inorganic carbon. In low-Na+ conditions, Na+ fluxes are too low to support the observed net 14C-carbon fixation rate. Active transport of HCO3- hyperpolarizes (not depolarizes) the membrane potential.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=158090Documentos Relacionados
- Genetically engineered mutant of the cyanobacterium Synechococcus PCC 7942 defective in nitrate transport
- Nitrite-Specific Active Transport System of the Cyanobacterium Synechococcus sp. Strain PCC 7942
- Identification of an ATP-binding cassette transporter involved in bicarbonate uptake in the cyanobacterium Synechococcus sp. strain PCC 7942
- Ethoxyzolamide Inhibition of CO2-Dependent Photosynthesis in the Cyanobacterium Synechococcus PCC7942 1
- Carbonic Anhydrase Activity Associated with the Cyanobacterium Synechococcus PCC7942 1