The interaction of H+-ATPase complex ***.F0 and the Trk system of K+ accumulation was studied in Escherichia coli grown quasi-anaerobically in peptone media with glucose (anaerobia) and aerobically in salt medium with...
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The interaction of H+-ATPase complex ***.F0 and the Trk system of K+ accumulation was studied in Escherichia coli grown quasi-anaerobically in peptone media with glucose (anaerobia) and aerobically in salt medium with succinate (aerobia). In anaerobia the Trk system takes part in H+-K+ exchange, displaying km = 3.7 mM, vmax = 1.6 mM g-1 min-1 and in aerobia in the Trk system has Km = 3.4 mM, vmax = 0.45 mM g-1 min-1. The K+ accumulation is blocked by DCC in anaerobia and by cyanide together with DCC in aerobic, whereas protonophores and arsenate block the K+ uptake in bacteria grown under either condition. Valinomycin decreases the K+ accumulation in anaerobic and increases (or has no effect) that in aerobia. ***.F0 is sensitive and the Trk system is insensitive to variation of the external osmotic pressure in both cases. The ratio H+:K+ is stable and equal to 2:1 in anaerobia and is changed from 0.5 to 5.0 in aerobia in response to variation of pH, K+ activity and temperature. Q10 is about 2.8 both for ***.F0 and for the Trk system in anaerobia, but 2.4 and near 1.0 respectively in aerobia. The distribution of K+ in anaerobia is 2500 (potassium equilibrium potential of -210 mV) which is much more than the measured Um of -145 mV. The distribution of K+ in aerobia is 720, which is in good conformity with the measured membrane protential of -175 mV. The structural association of ***.F0 and the Trk system, forming a H+-K+ pump, has been assumed previously to take place in anaerobically grown E. coli;these systems operate separately in aerobic cells. According to Bakker and Helmer et al. the Trk system transport K+ along the electrical field, its function being regulated by ATP.
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