Ammonium (methylammonium) transport by Klebsiella pneumoniae.

Klebsiella pneumoniae can accumulate methylammonium up to 80-fold by means of a transport system as indicated by the energy requirement, saturation kinetics and a narrow pH profile around pH 6.8. Methylammonium transport (apparent Km = 100 microM, V = 40 mumol/min per g dry weight at 15 degrees C) is competitively inhibited by ammonium (apparent Ki = 7 microM). The low Ki value and the finding that methylammonium cannot serve as a nitrogen source indicate that ammonium rather than methylammonium is the natural substrate. Uphill transport is driven by a component of the protonmotive force, probably the membrane potential. The transport system is under genetic control; it is partially repressed by amino acids and completely by ammonium. Analysis of mutants suggest that the synthesis of the ammonium transport system is subject to the same 'nitrogen control' as nitrogenase and glutamine synthetase.