FIG. 2.
Kinetic parameters of glycine betaine uptake under hyperosmotic and osmostatic conditions. L. lactis IL1403 cells grown in CDM (without proline) plus 25 mM glucose and 500 mM KCl were washed and resuspended in 50 mM KPi, pH 6.5. Prior to the initiation of transport, IL1403 cells were pre-energized for 5 min with 10 mM glucose. Uptake of [14C]glycine betaine was assayed in 50 mM KPi, pH 6.5, with (■) or without (●) 500 mM KCl. The uptake rates were determined in the concentration range of 0.1 μM to 1.25 mM, but only the data up to 20 μM are shown. The transport assays were stopped after 10 s by diluting the samples 20-fold with ice-cold assay buffer of the corresponding osmolarity; this was followed by rapid filtration and washing of the filters. The data were analyzed with the Michaelis-Menten equation. The Km values were 1.7 and 1.5 μM in the presence and absence of 500 mM KCl, respectively.