The LRET lifetimes measured at 510 nm for donor:acceptor-tagged receptors. Lifetimes are shown for (A) ΔN*-GluR4-G740C, (B) ΔN*-GluR4-G740C-L484Y, (C) ΔN*-GluR4-S741C, (D) ΔN*-GluR4-S741C-L484Y, (E) ΔN*-GluR4-S742C, and (F) ΔN*-GluR4-S742C-L484Y receptors expressed in oocytes in the absence of agonists (black), with 10 mM glutamate (green), and with 10 mM glutamate in the presence of 100 μM cyclothiazide (red). Lifetimes after subtraction of the residual lifetimes upon thrombin digestion for (G) ΔN*-GluR4-Th-S741-Th and (H) ΔN*-GluR4-Th-S741-Th-L484Y receptors expressed in HEK-293 cells in the absence of agonists (black), with 10 mM glutamate (green), with 10 mM glutamate in the presence of 100 μM cyclothiazide (red), and in the presence of 200 nM antagonist ZK200775 (blue).