mTOR exists as two types of complexes called mTORC1 and mTORC2. mTORC1 is regulated in activity by amino acid and inhibited specifically by a immunosuppressant “rapamycin”. It is considered that PRAS40 is phosphorylated by mTORC1, for phosphorylation of PRAS40 (proline-rich Akt substrate of 40 kDa) which is a novel substrate of mTOR at Ser-183 (human) is induced by amino-acid stimulation and inhibited by rapamycin.