| The catalytic domain of serum and glucocorticoid regulated protein kinase ( SGK ) is 54 % identical with that of PKB and , although lacking the PtdIns ( 3 , 4 , 5 ) P 3 binding pleckstrin homology domain , SGK retains the residues that are phosphorylated by PDK 1 and PDK 2 , which are Thr 256 and Ser 422 in SGK . ^^^ Our results are consistent with a model in which activation of SGK by IGF 1 or hydrogen peroxide is initiated by a PtdIns ( 3 , 4 , 5 ) P 3 dependent activation of PDK 2 , which phosphorylates Ser 422 . ^^^ |