RAB proteins have intrinsic weak GTPase activity that is enhanced by RAB-GTPase activating proteins (RAB-GAPs, Sano et al. 2007). The GTPase activity of RAB13 is inferred from other RAB proteins. AS160 (TBC1D4) and TBC1D1 are GAPs that activate the GTPase activity of RAB8A/10/13. Insulin signaling activates AKT, which phosphorylates and inactivates AS160 and TBC1D1, allowing GTP-bound (active) RABs to accumulate.