signaling pathway that leads to cell growth

Akt is a key protein kinase in the signaling pathway that leads to cell growth. Akt is activated by a phosphatidylinositol-dependent protein kinase (PDK1), which phosphorylates threonine 308. At the same time, serine 473 is phosphorylated. Your advisor has been unsuccessful in purifying the protein kinase responsible for the phosphorylation of serine 472, but you think you know what is going on. You construct genes encoding two mutant forms of Akt: one carries a point mutation in the kinase domain, Akt-K179M, which renders it kinase-dead, and the other carries a point mutation in the domain required to bind to PDK1 (Akt-T308A), which cannot be activated by PDK1. You transfect each of these constructs, and a construct for wild-type Akt, into cells that do not express their own Akt. You treat a portion of the cells with an insulin-like growth factor (IGF1), which activates PDK1, and analyze the phosphorylation state of the various forms of Akt using antibodies specific for Akt or for particular phosphorylated amino acids (see blot on the right). What is the identity of the enzyme that phosphorylates serine 473 on Akt (1 point, write enzyme)? Explain your reasoning (3 points, 2-3 sentences).