TABLE 4

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

Compound% activity
No inhibitor100
Amino acidsa
    l-cysteine45 ± 2
    dl-homocysteine58 ± 2
    l-methionine76 ± 2
    Glycine90 ± 3
    l-proline100 ± 1
    l-valine85 ± 2
    l-leucine97 ± 1
    l-phenylalanine89 ± 1
    l-serine100 ± 1
    l-glutamine99 ± 4
    l-gluatamic acid98 ± 3
    l-lysine89 ± 1
Sulphur compoundsa
    l-cysteamine HCl92 ± 10
    dl-cysteic acid111 ± 15
    l-glutathione98 ± 2
    l-cystineb102 ± 3
    l-cystathionineb104 ± 4
    Buffer (50 mm KCl–HCl pH 1)b109 ± 2
Metabolic inhibitorsc
    Sodium azide (40 μm)64 ± 5
    Sodium azide (100 μm)42 ± 4
    CCCP (40 μm)d62 ± 5
    CCCP (100 μm)d48 ± 1
    DMSOd101 ± 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).

  • a All 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.

  • b l-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.

  • c Cells were preincubated with the indicated concentrations of metabolic inhibitors for 15 min prior to the addition of the uptake medium.

  • d CCCP was dissolved in DMSO and hence DMSO was analyzed for its effect on cysteine uptake by the cells.