FIG. 3.

Uptake of phosphate by porin mutants of M. smegmatis. (A) Accumulation of [³²P]phosphate by M. smegmatis SMR5 (wild-type) (black circles), the ΔmspA ΔmspC mutant ML10 (white circles), and ML10 complemented with the mspA expression plasmid pMN016 (triangles) was measured. The assay was performed at 37°C at a final phosphate concentration of 20 μM. The uptake rates were determined by a regression analysis of the first 4 min for each strain. The dotted lines represent regression lines. Error bars indicate standard deviations. (B) A series of phosphate uptake measurements was performed with phosphate concentrations ranging from 1 to 20 μM for M. smegmatis SMR5 (wild-type) and ML10 (ΔmspA ΔmspC). For each strain, the uptake rates at different phosphate concentrations were approximated by Michaelis-Menten functions that are shown as regression lines (dotted lines).