An electrochemical study of energy-dependent potassium accumulation in E. coli Part 14. Comparison of K + uptake characteristics in anaerobically grown cells performing glycolysis or nitrate/nitrite respiration: role of the respiratory chain

Abstract

The characteristics of H +−K + exchange in anaerobically grown wild-type Escherichia coli K12(λ) performing nitrate/nitrite respiration are studied and compared with H +−K + exchange in cells performing glycolysis. Unlike glycolysing cells, in which H +−K + exchange takes place in two steps with different characteristics and inhibitor effects, H +−K + exchange in E. coli K12(λ) with nitrate/nitrite respiration requires only one step. K + uptake with a K m of 4.5 mM is not sensitive to N, N′-dicyclohexylcarbodimide (DCCD), but is inhibited by arsenate or protonophore. Such a K + uptake is observed in the trkG mutant and is absent in the mutant with the trkA deletion. K + accumulation is greater than 270 mM and the K + gradient between the cytoplasm and the medium is comparable with the measured Δφ. The ratio of H + to K + flux through the membranes in the absence or presence of DCCD varies with the change in K + external activity. A DCCD-sensitive ATPase activity in the isolated membranes of the trkG mutant is not stimulated by K +; such activity was lost in the trkG mutant with the deletion of the unc-operon. Moreover, H 2 production by respiring cells is not observed. In addition, K + uptake is osomosensitive and occurs under an upshock (i.e. an increase in the osmolarity of the medium). This osmosensitivity is lost in spheroplasts deprived of periplasmic space. The K +-uptaking TrkA system in E. coli worked as an ATP-driven pump by association with F 1F 0 in the united mechanism in glycolysing bacteria, and is assumed to operate as an uniport using ΔμH in cells with nitrate/nitrite respiration. This system has no ATPase activity and cannot carry out intramolecular dithiol-disulfide interconversion leading to H 2 production. The interaction of the TrkA system with the F 1F 0 within the membrane is determined by a respiratory chain. This system is osmosensitive in anaerobically grown cells; osmoregulation can occur in a periplasmic space.