[Independent functioning of the H+-K+ ion exchange systems in E. coli]

Two systems of potassium accumulation inhibited by N,N1-diciclohexilcarbodiimide (DCCD) can operate simultaneously and independently in the strain E. coli TK 1001. These are the TrkA and TrkF systems. The strain E. coli TK 509 demonstrates only the TrkF system in the media with potassium concentrations higher than 1 meg. 1-1. The onset of K+-uptake via the TrkF is observed much earlier than that in E. coli TK 1001. Moreover the secretion of H+ increases considerably with the start of K+-uptake. 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 possess at least two proton-potassium exchanging systems (TrkA and TrkF) sensitive to DCCD. The TrkA system operates a short time in response to an increase of the osmolarity in the medium and exchanges rapidly 2H+ for 1K+, whereas the TrkF maintains a slow exchange of H+ for K+ with the unstable ratio H+/K+ from 4 to 14.