FIG. 7.

Involvement of the cyanobacterial CCM in cyanate metabolism. (A) Time course of KOCN-dependent ¹²CO₂ efflux in the light (solid lines) and dark (dashed lines). S. elongatus strain PCC7942 ΔchpX ΔchpY cells grown on 5% CO₂ were suspended in 100 mM EPPS (N-[2-hydroxyethyl]piperazine-N′-[3-propanesulfonic acid]) buffer, pH 8, and incubated in the light or dark for 5 min in the reaction cuvette, in the absence and presence of 10 mM NaH¹³CO₃ (¹³C_i). The experiment was started by the addition of 1 mM KOCN, and ¹²CO₂ efflux was measured over time by MS. (B) Dependence of ¹²C_i efflux rate on ¹³C_i concentration. The average rate of ¹²C_i efflux, at a constant cell density (7.5 μg of Chl a ml⁻¹), was calculated from ¹²CO₂ efflux measurements over an 8-min interval as a function of ¹³C_i concentration for ΔchpX ΔchpY (chpXY) cells in the light (•) and dark (○) provided with 1 mM KOCN. Also shown (dashed line and ▴) is the dependence on ¹³C_i concentration of ¹²CO₂ efflux in S. elongatus PCC7942 wild-type (WT) cells grown under low-C_i conditions.