TABLE 2.

Effects of potential competitive inhibitors, inhibitors of energy generation, and thiol-containing enzymes on short-term uptake of [¹⁴C]choline in an estuarine filtrate culture^a

Inhibitor	Percent uptake in controlb
Competitive inhibitorsc
Control (no addition)	100 ± 4
Glucose	102 ± 2
Ethanolamine	91 ± 4
l-Proline	82 ± 6
Glycine	79 ± 7
l-Proline	75 ± 4
Dimethylglycine	68 ± 3
Proline betaine	54 ± 4
Carnitine	50 ± 1
GBT trial 1	41 ± 2
DMSP trial 1	40 ± 2
DMSP trial 2	36 ± 1
GBT trial 2	36 ± 1
Choline trial 1	14 ± 1
Choline trial 2	10 ± 1
Energy uncouplers or thiol-binding reagentsd
DNP	71 ± 3
Sodium azide	72 ± 3
p-CMB	4 ± 3

^aFiltrate culture was generated by filtering water through a GF/F filter by gravity. The culture, containing mainly free-living bacteria, was preincubated for 24 h in the dark prior to choline uptake assays. 

^bValues represent the means of duplicate determinations of total uptake of [¹⁴C]choline into filterable material, expressed as a percentage of the controls. The error terms indicate the range about the mean. The total uptake in controls ranged from 640 to 702 dpm · 10 ml of sample⁻¹ depending on the trial. Incubation was carried out for 20 min. 

^cCompetitive inhibitors were added at 200 nM immediately before the addition of 9.4 nM [¹⁴C]choline. 

^d2,4DNP, azide, and p-CMB were added at 100 μM 1 h before the addition of 9.4 nM [¹⁴C]choline.