Active Pak colocalizes with p22^phox in the plasma membrane. Cos cells expressing p22^phox were transfected with wild-type Myc-Pak1 or Myc-Pak1 F107, E423 for 24 hours and prepared for confocal microscopy. Human monocytes were differentiated into macrophages in vitro and either left untreated or stimulated with 1 μM fMLF for 3 minutes. Localization of proteins in all panels was assessed by confocal microscopy after fixation and costaining for Pak and p22^phox. A representative image of 2 independent experiments is shown.