Figure 3. Effects of the GS inhibitor MSF on [¹⁴C]MA uptake.

(A) Inhibition of GS by MSF. GS activity was measured by calculating the slope of the curve for [¹⁴C]methylglutamine accumulation in washed assays from time points at 30, 120, 180 and 240 s with or without MSF pre-treatments. MSF (1–100 μM) was added to cultures 4 min before starting the transport assays by adding [¹⁴C]MA. Results are expressed as percentage inhibition compared with the activity in the absence of MSF, and are means±S.D. (n=4). (B) Effect of MSF on MA uptake measured in unwashed assays. ET8000 (wild-type) without pre-treatment (◇), or pre-treated for 4 min with 20 μM MSF (◆), ET8004 (glnA⁻) (□), GT1000 (glnK⁻ amtB⁻) (△). Results are means±S.D. (n=4).