The characterization of energized and partially de-energized (respiration-independent) β-galactoside transport into escherichia coli

Unidirectional fluxes of [14C]lactose by whole cells of Escherichia coli under highly energized and partially de-energized (in the presence of CN−) conditions are analyzed kinetically. When the cells are energized, the value for V influx is 0.45 ± 0.01 mM internal concentration increment/s and Kt is 0.26 ± 0.03 mM. At an external concentration of 0.61 mM the steady-state internal concentration is 0.25 M, reached after about 1h. The maximum steady-state concentration ratio is 2 · 103. The efflux process under these conditions is non-saturable, being linearly dependent upon internal concentration over the range 25–250 mM with a first-order rate constant of 8.8 ± 0.2 · 10−4 s−1. The transport in the presence of CN− is active, with a maximum concentration ratio (internal concentration/external concentration) of 104, and the uptake is mimicked by anoxia (< 70 ppm O2). The effects of CN− are to lower the V for influx and to change the efflux from a non-saturable to a saturable process with a value for Kt (60 mM) intermediate between that for energized efflux (> 250 mM) and influxe (0.3–0.6 mM), the latter value not changing appreciably. Partial de-energization thus affects both the influx and efflux processes.