Akt, protein kinase B (PKB), is a serine/threonine kinase which is involved in many cellular signaling pathways and acts as a transducer of many functions initiated by growth factor receptors that activat phosphtidylinositol 3-kinase (PI 3-kinase). The major activity of Akt/PKB is to mediate cell survival. Akt/PKB is also believed to be a critical factor in the genesis of cancer as the tumor suppressor PTEN was found to antagonise PI-3 kinase and Akt/PKB kinase activity. There are 3 known isoforms of this enzyme in mammalian cells (1/alpha, 2/beta and 3/gamma). Akt1, 2 and 3 contain a key regulatory serine phosphorylation site in the carboxy-terminal region of the protein. Akt/PKB phosphorylation is critical for it activity.