When cellular energy is depleted, the active AMPK complex (bound to AMPK, AMPK alpha phosphorylated on Thr-172 or Thr-174) phosphorylates the mTORC1 component RPTOR (Raptor) on Ser-722 and Ser-792. These phosphorylations are required for inhibition of mTORC1 activity in response to energy stress (Gwinn et al. 2008), and are believed to promote the dissociation of mTORC1 from the ULK1 complex (Wong et al. 2013). This reduces mTORC1 phosphorylation of ULK1 Ser-758, which consequently is able to associate with, and be activated by, AMPK (Egan et al. 2011). This coordinated phosphorylation of ULK1 by mTORC1 and AMPK may provide a mechanism by which cells can properly respond to a wide range of stimuli.
AMP-activated protein kinase activity of p-AMPK heterotrimer:AMP [cytosol]