l‐threonine transport in the obligate methylotroph Methylobacillus flagellatum KT

The accumulation of l‐threonine by the methylotrophic bacterium Methylobacillus flagellatum KT occurs via a specific system that is capable of transporting l‐threonine against a 100‐fold concentration gradient. This transport system demonstrates the following kinetic parameters: Km= 0.2 mM and Vmax= 2.5 nmol/min/mg of cells (dry weight). The activity of the system is inhibited by oxidative phosphorylation uncouplers and valinomycin. Cytoplasmic l‐threonine does not leak from the cell, but bacteria are capable of exchanging exogenous l‐threonine for its intracellular counterpart.