TABLE 4.

Effect of various compounds on cysteine uptake in the met15Δ gnp1Δ mup1Δ triple-delete strain

Compound	% activity
No inhibitor	100
Amino acidsa
l-cysteine	45 ± 2
dl-homocysteine	58 ± 2
l-methionine	76 ± 2
Glycine	90 ± 3
l-proline	100 ± 1
l-valine	85 ± 2
l-leucine	97 ± 1
l-phenylalanine	89 ± 1
l-serine	100 ± 1
l-glutamine	99 ± 4
l-gluatamic acid	98 ± 3
l-lysine	89 ± 1
Sulphur compoundsa
l-cysteamine HCl	92 ± 10
dl-cysteic acid	111 ± 15
l-glutathione	98 ± 2
l-cystineb	102 ± 3
l-cystathionineb	104 ± 4
Buffer (50 mm KCl–HCl pH 1)b	109 ± 2
Metabolic inhibitorsc
Sodium azide (40 μm)	64 ± 5
Sodium azide (100 μm)	42 ± 4
CCCP (40 μm)d	62 ± 5
CCCP (100 μm)d	48 ± 1
DMSOd	101 ± 5

The rate of uptake of cysteine (40 μm) was measured in met15Δ gnp1Δ mup1Δ in the presence of the different compounds listed in the table. The cells were harvested at 30- and 90-sec intervals. The results were normalized to the rate of uptake measured in the absence of any other compound (no inhibitor). Data are shown as mean ± SD (n = 4).

^aAll competitors were added to a final concentration of 800 μm in a 10-μl volume, i.e., 20-fold excess over the labeled substrate, and were added simultaneously with uptake medium.

^bl-cystine and l-cystathionine were dissolved in buffer (50 mm KCl–HCl, pH 1); hence the buffer was analyzed for its effect on cysteine uptake by the cells.

^cCells were preincubated with the indicated concentrations of metabolic inhibitors for 15 min prior to the addition of the uptake medium.

^dCCCP was dissolved in DMSO and hence DMSO was analyzed for its effect on cysteine uptake by the cells.