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

Abstract

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 K t 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 · 10 3 . 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 O 2). 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 K t (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.