| Comments |
P.5694 left column bottom paragraph: "Kinetics of TDG [β-D-galactopyranosyl 1-thio-β-D-galactopyranoside] Transport: The data presented in Figure 1 are representative kinetics for the transport of TDG, an uncharged, high-affinity substrate of the lac transport system in E. coli. At pH 5.5, with both electrical (Δѱ) and chemical (ΔpH) components of ΔµH+ available (open circles), the initial rate of transport increases as a saturable function of TDG concentration, and a straight line is observed in the V vs. V/S plot. The apparent Km derived from the slope of the function is 16µM, and the Vmax estimated from the y intercept at infinite TDG concentration is 10.3 nmol/(min mg of protein). When valinomycin is added under conditions that dissipate Δѱ with a small increase in ΔpH and a 50% decrease in ΔµH+ (Table I), the apparent Km remains unchanged, while Vmax decreases to about 6.6 nmol/(min mg of protein) (closed circles). Similarly, in the presence of nigericin which abolishes ΔpH, increases Δѱ, and leaves ΔµH+ at 70% of maximum (Table I), Vmax is diminished to about 5 nmol/(min mg of protein), and the apparent Km remains constant (open triangles)." See note beneath table |