PKA (or cAPK) is a cyclic AMP dependent protein kinase. When activated by the second messenger cAMP, PKA mediates diverse cellular mechanisms, including proliferation, ion transport, regulation of metabolism, plus gene transcription. PKA is comprised of two dimers of two subunits, R (regulatory) and C (catalytic). Two families of R subunit (RI and RII) and three C subunit isoforms (C alpha, C beta, and C gamma) have been identified each possessing distinct cAMP binding properties and resul