TABLE 2.

Kinetic parameters of glycine betaine and proline uptake in wild-type L. plantarum ATCC 14917 and a DHP-resistant mutant^a

Uptake	Strain	Culture conditions	Low-osmolality assay conditions		High-osmolality assay conditions
			Km (μM)	Vmax (nmol/min/mg of protein)	Km	Vmax
Glycine betaine	Wild type	CDM	18 ± 2	27 ± 3	33 ± 6	105 ± 6
		CDM − Pro	19 ± 4	86 ± 5	26 ± 6	116 ± 6
	DHPR-38.1	CDM	6 ± 2	2 ± 0.5	12 ± 3	9 ± 0.5
		CDM − Pro	22 ± 6	7 ± 0.5	22 ± 3	9 ± 0.5
	Wild type	CDM + KCl	13 ± 3	35 ± 2	33 ± 6	106 ± 6
		CDM − Pro + KCl	17 ± 4	125 ± 9	23 ± 7	198 ± 20
Proline	Wild type	CDM	950 ± 150	21 ± 2	1,500 ± 150	150 ± 8

^aFollowing growth in the indicated media (− Pro, proline omitted from CDM; + KCl, 0.8 M KCl added to CDM), the cells were washed and resuspended to a final protein concentration of 0.4 to 0.8 mg/ml in 50 mM potassium phosphate (pH 6.5). The [¹⁴C]glycine betaine and [¹⁴C]proline concentrations were in the range of 0.9 μM to 10 mM. After 7 min of preenergization with 10 mM glucose, uptake was initiated by the addition of [¹⁴C]glycine betaine or [¹⁴C]proline with (high-osmolality assay conditions) or without (low-osmolality assay conditions) 0.8 M KCl. After 30 s of uptake, the cells were rapidly filtered and processed further as described in Materials and Methods. The data from two separate experiments were used to calculate the arithmetical average of the uptake rates; standard deviations are also shown.