FIG. 4.

Predictions of 2,4-D uptake rates by the diffusion model for the tfdK mutant and by the two models for TfdK-mediated transport in wild-type R. eutropha JMP134(pJP4) cells. (A) Influence of TfdA activity for different values of V_max,TfdA (51, 46, 41, and 36 nmol · min⁻¹ · mg of protein⁻¹) on uptake rates by the tfdK mutant (dotted lines) and wild-type cells (solid lines) at different assay concentrations. For the wild type, the curves for active transport and facilitated diffusion overlap; therefore, only one is shown. (B) Intracellular accumulation of 2,4-D, i.e., [2,4-D]_in/[2,4-D]_out, in the tfdA mutant (V_max,TfdA of 0 nmol · min⁻¹ · mg of protein⁻¹) and with an apparent permeability coefficient for 2,4-D of 1.8 × 10⁻⁴ liters · min⁻¹ · mg of protein⁻¹, assuming either active transport (V_max,TfdK, 20 nmol · min⁻¹ · mg of protein⁻¹; K_m,TfdK, 5 μM [equation 6]) or facilitated diffusion (V_max,TfdK, 160 nmol · min⁻¹ · mg of protein⁻¹; K_m,TfdK, 4 μM [equation 5]).