PKA (Protein Kinase-A) is a second messenger-dependent enzyme that has been implicated in a wide range of cellular processes, including transcription, metabolism, cell cycle progression and apoptosis. Known modulators of PKA activity include factors that either activate or inhibit AC (Adenylate Cyclase), resulting in an increase or decrease in cAMP (Cyclic Adenosine 3',5'-monophosphate) levels. The enzyme occurs naturally as a four-membered structure with two regulatory (R) and two catalytic (C) subunits. Four genes encode the R...