Channel-mediated permeation of ammonia gas through the peribacteroid membrane of soybean nodules

Ammonia permeability of the peribacteroid membrane (PBM) from N-2-fixing soybean nodules was measured (8 x 10(-5) m/s) using isolated PBM in a stopped-flow spectrofluorimeter, Ammonia (NH,) uptake into PBM vesicles,vas inhibited by up to 42% bg HgCl2 (EC50 = 2.9 mu M, mercaptoethanol-reversible) and reduced by ATP pre-incubation, The activation energy of NH3 uptake (52 kJ/mol) increased (118 kJ/mol) with HgCl2. Water transport was also HgCl2-sensitive (EC50 = 52.6 mu M), but increased by ATP pre-incubation. NH3 and H2O may permeate via different pathways through Nodulin 26 or there is another protein on the PBM that is permeable to NH3. (C) 2000 Federation of European Biochemical Societies.