Figure 5.

Investigating the acidity of intracellular compartments during folate-FR trafficking using FRET. The folate-FRET reporter #2 emits green fluorescence upon acid-induced cleavage. After a 0.5-h incubation with 100 nM of reporter #2 and a subsequent wash step to remove unbound conjugates, KB cells were imaged with confocal microscopy after (a) 1.5, (b) 5.5, or (c) 18.5 h of further incubation in culture medium by excitation at 488 nm.123 Copyright © 2007 American Society for Pharmacology and Experimental Therapeutics