Effect of uncouplers on "downhill" beta-galactoside transport in energy-depleted cells of Escherichia coli

Abstract

Galactoside permease-containing cells of Escherichia coli can be depleted of energy reserves so that the "downhill" cellular hydrolysis of o-nitrophenyl-beta-d-galactopyranoside (ONPG) no longer takes place. Treatment of such energy-depleted cells with proton-conducting agents such as carbonylcyanide m-chlorophenylhydrazone results in stimulation of ONPG transport. The same agents lower transport of non-energy-depleted cells towards the same levels that result from stimulation of the energy depleted cells. Of course, these agents prevent "uphill" accumulation against a concentration gradient under all conditions. Since uncouplers allow normal and energy-depleted cells to assume the same facilitated transport capability, these results lend support to the chemiosmotic hypothesis of Mitchell that comigration of charge is necessary for the transport of neutral galactosides. Our results imply that a potential favorable to transport is maintained by metabolism in non-energy-depleted cells, whereas an unfavorable potential is developed in the initial instant of time when energy-depleted cells are given ONPG.