Methylammonium transport in Anacystis nidulans R-2.
Methylammonium was taken up rapidly by illuminated cells of Anacystis nidulans R-2, leading to internal concentrations of 1.3 +/- 0.1 mM within 1 min, and a gradient of up to 200 between the cells and medium. Accumulation of 14CH3NH3+ required at least 5 mM NaCl, but the uptake rate was independent of medium pH between 6.5 and 9. The kinetics of uptake could be resolved into an initial fast phase lasting less than 1 min (approximate Km, 7.2 microM; Vmax, 12.5 nmol min-1 mg of protein-1 at 15 degrees C). A second, slower phase associated with product formation was eliminated by preincubation with methionine sulfoximine, a specific inhibitor of glutamine synthetase; the rapid phase was unaffected by this treatment. Ammonium ions competed with 14CH3NH3+ for entry, and addition of 5 microM NH4+ or 100 microM CH3NH3+ released 14CH3NH3+ accumulated during the rapid phase of entry. Small additions of NH4+ made at the same time as additions of 14CH3NH3+ delayed the start of radioactivity uptake by a time which corresponded accurately with the period needed for the complete removal of the added NH4+. The effects of inhibitors on accumulation and carbocyanine dye fluorescence suggest that ATP-dependent membrane potential was needed to drive 14CH3NH3+ transport. Spheroplasts were as active as whole cells in accumulating NH4+ and 14CH3NH3+, indicating that soluble periplasmic components are not involved in the translocation. Some significant differences between the translocation of 14CH3NH3 and that of NH4+ were observed: growth with NH4+ in place of NO3- repressed 14CH3NH3+ accumulation ability without affecting the NH4+ uptake rate Na+ was not required for NH4+ uptake, and concentration of KCl inhibitory with 14C3NH3+ did not reduce NH4+ uptake.
D000469:Alkaline Phosphatase / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D000458:Cyanobacteria / Q000378:metabolism*; D007700:Kinetics; D008744:Methylamines / Q000378:metabolism*; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000494:pharmacology; D013104:Spheroplasts / Q000378:metabolism
D002250:Carbon Radioisotopes; D008744:Methylamines; D012965:Sodium Chloride; D000641:Ammonia; C027451:methylamine; D000469:Alkaline Phosphatase