Methylammonium uptake by Escherichia coli: evidence for a bacterial NH4+ transport system.

Energy-dependent concentrative uptake of ¹⁴CH₃NH₃⁺ by cells of $\text{Escherichia coli}$ provides preliminary evidence for one or more transport systems for NH₄⁺ uptake. NH₄⁺, but not glutamic acid, inhibited the uptake of ¹⁴CH₃NH₃⁺. Varying the pH for the uptake assays exposed two apparent systems: one maximally functioning at pH 7 that was strongly inhibited by cyanide or by the uncoupler $\text{m}$-chlorophenyl carbonylcyanide hydrazone and another maximally functioning at pH 9 and resistant to cyanide or $\text{m}$-chlorophenyl carbonylcyanide hydrazone. Kinetic analysis showed considerable experimental variability from day to day. Often simple Michaelis-Menten kinetics were not followed, but NH₄⁺ was reproducibly a stronger inhibitor of uptake of ¹⁴CH₃NH₃⁺ than was nonradioactive CH₃NH₃⁺.