HCO3- AND CO2 LEAKAGE FROM SYNECHOCOCCUS UTEX-625

The leakage of various inorganic carbon species from air-grown cells o f Synechococcus UTEX 625 was investigated after a light to dark transi tion or during a light period using a mass spectrometer under a wide v ariety of experimental conditions. Total inorganic carbon efflux and C O2 efflux during the initial period of darkness were measured with or without carbonic anhydrase in the reaction medium respectively. The HC O3- efflux after a light to dark transition was estimated by differenc e. Carbon dioxide efflux in the light was measured by inhibiting CO2 t ransport with either Na2S or COS, or quenching the C-13 inorganic carb on transport by the addition of C-12 inorganic carbon in excess, in ce lls in which CO2 fixation was inhibited, when only the HCO3- transport system was fully operative, CO2 effluxed continuously during the ligh t period at a rate equal to about 25% of that in darkness, When only t he CO2 transport system was operative, HCO3- effluxed during the light period, The difference between the light and dark efflux rates was co nsistent with a 0.6 unit decrease in the intracellular pH upon darkeni ng the cells. The permeabilities of the cell for CO2 (2.94 +/- 0.14 x 10(-8) ms(-1); mean +/- SE, n = 137) and HCO3- (1.4-1.7 x 10(-9) ms(-1 )) were calculated.