Despite Apt1 being identified many years ago, the physiological importance of this protein as a thioesterase is not clear. However, a recent study reported an important function for Apt1 in controlling dendritic spine volume, possibly by regulating palmitoylation and membrane localization of G 13 (Siegel et al., 2009 ). The recent description of a novel Apt1 inhibitor (palmostatin B) should provide an important tool to more finely dissect the function of this protein in cellular palmitoylation dynamics (Dekker et al., 2010) . Initial analysis with palmostatin B suggests that it promotes a moderate increase in Ras palmitoylation and disrupts the intracellular localization of this protein.