An electrochemical study of energy-dependent potassium accumulation in E. coli: VI. Identification of H +−K +-exchanging systems

Abstract

It has been shown on a wild strain E. coli K-12(λ) that two systems of potassium accumulation inhibited by DCCD can operate simultaneously and independently. They are the TrkA and TrkF systems [9] as discovered by means of the mutant E. coli TK 1001. Another mutant, E. coli TK 509 manifests only the TrkF system in media with potassium concentrations>1 meq/dm 3 and the onset of K + -uptake via the TrkF is observed much earlier than that in E. coli K-12(λ) or TK 1001. Moreover, the secretion of H + increases considerably with the start of K + -uptake. The DCCD-sensitive and counter-directed fluxes of H + and K + enhance proportionally both the increase of external potassium concentration and pH. Thus, the E. coli cells posses at least two proton-potassium exchanging systems ( TrkA and TrkF ) sensitive to DCCD. The TrkA system operates for 2–5 min in response to the increase of the osmolality in the medium and rapidly exchanges 2 H + for 1 K + whereas the TrkF maintains a slow exchange of H + for K + with the unstable ratio H + :K + from 4 to 14.