As a member of the family of GTPases, Ras proteins officiate as molecular switches (i.e. cycling between a GDP-bound OFF and a GTP-bound ON state) in many signal transduction cascades. Oncogenic mutations in Ras genes can lead to constitutively active proteins, which are found in 20-30% of all human tumors. Interfering with Ras localization at the plasma membrane would disturb the oncogenic proliferation signal, making Ras a potential anti cancer target. There are three human Ras isoforms (H/N/K), which are all posttranslationally prenylated. H- and N-Ras are additionally S-palmitoylated. Both modifications increase the hydrophobicity and therefore the membrane affinity of Ras. The reversibility of palmitoylation allows the spatial regulation of Ras via a reaction-diffusion mechanism called “acylation cycle”. This is achieved by an ubiquitous depalmitoylation of Ras followed by a rapid diffusion to the golgi apparatus where it gets palmitoylated and transferred back to the plasma membrane via a vesicular transport. This cycle ensures the enrichment of Ras on the plasma membrane and prevents its mislocalization on other cellular membranes.The depalmitoylation of Ras is catalyzed by the Acyl Protein Thioesterase (APT). Its function is to prevent mislocalization of H- and N-Ras to the endomembranes and it allows the acylation cycle to reestablish the physiological plasma membrane localization. Inhibiton of APT inhibits this cycle and Ras remains distributed on the endomembranes. The absence of Ras from the plasma membrane leads to a weaker Ras mediated proliferation signal. APT itself undergoes a dynamic palmitoylation for steady state membrane localization.The effect of membranes on APT and their targets remains still unclear. In the presented work, several biochemical methods were used to investigate how the physiological membrane environment influences the APT activity.