TABLE 2.

Phosphate uptake parameters and selenite inhibition constants of wild-type and P_i transporter-defective strains

The uptake experiments were performed as described under “Experimental Procedures” on two independently grown cultures, apart from BY4742 grown in 0.3 mm P_i (four independent experiments), BY4742 grown in 7.3 mm P_i, and Δspl2 grown in 0.3 mm P_i (three independent experiments). Seven different concentrations of phosphate were used to determine the kinetic parameters. The P_i concentrations were in the range 5–500 μm for high affinity uptake and 0.1–7.5 mm for low affinity uptake measurements. To determine the phosphate uptake parameters in the Δspl2 strain, 10 concentrations of phosphate were used (5–5000 μm). Selenite inhibition constants were determined from the measurements of the apparent K_m for phosphate in the presence of 2.5, 5, and 10 mm selenite. The K_i was deduced from the slope of the plot of K_m^app as a function of selenite concentration. The errors are standard deviations.

Pi concentration	Strain	Vmax	Km	Ki
		pmol Pi·min−1·OD650−1	μm	mm
0.3 mm	BY4742	860 ± 80	20 ± 4	4.6 ± 1.7
0.3 mm	Δpho87-Δpho90-Δpho91	2000 ± 300	25 ± 3	5.5 ± 1.8
0.3 mm	Δspl2	Vmax 1 600 ± 140	Km 1 19 ± 6
		Vmax 2 1700 ± 400	Km 2 4000 ± 1300
0.3 mm	Δpho84	700 ± 150	5000 ± 1600
0.3 mm	Δpho84-Δspl2	1400 ± 300	5900 ± 1800
7.3 mm	BY4742	1600 ± 400	4300 ± 1600	9.0 ± 2.0
7.3 mm	Δpho87	440 ± 50	25 ± 6
7.3 mm	Δpho84	1700 ± 200	6000 ± 2000	9.5 ± 2.0
7.3 mm	Δpho84-Δspl2	2000 ± 500	5800 ± 2000