title: Ammonium and methylammonium transport by the nitrogen-fixing bacterium Azotobacter vinelandii.
abstract: Azotobacter vinelandii, grown with NH4+ as nitrogen source, was shown to possess an active transport system which can take up NH4+ against a concentration gradient of 58-fold. The properties of the NH4+ uptake system were investigated with the NH4+ analog CH3NH3+. The use of this analog was justified on the basis of the conclusion that the uptake of NH4+ and CH3NH3 involves a common binding site, as shown by the competitive inhibition of CH3NH3+ uptake by NH4+ (Ki approximately 3 microM). A Lineweaver-Burk plot for CH3NH3+ uptake revealed a biphasic curve, suggesting the existence of two CH3NH3+ (NH4+) uptake systems with apparent Km's for CH3NH3+ equal to 61 microM and 661 microM. The uptake of CH3NH3+ was inhibited by arsenate, as well as by cyanide or carbonyl cyanide-m-chlorophenyl hydrazone, indicating that phosphate bond energy is required.
mesh_terms: D001149:Arsenates / Q000494:pharmacology; D001395:Azotobacter / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D007700:Kinetics; D008744:Methylamines; D009584:Nitrogen / Q000378:metabolism; D011190:Potassium Cyanide / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
chemical_list: D001149:Arsenates; D008744:Methylamines; D000644:Quaternary Ammonium Compounds; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; C027451:methylamine; D011190:Potassium Cyanide; D009584:Nitrogen; C025657:arsenic acid