Differentiate between PKA and PKG.

PKA :

1. Protein kinase-A (PKA) is a family of enzymes whose activity is dependent on cellular level of cyclic AMP (cAMP).
2. PKA is also known as cAMP dependent protein kinase.
3. Inactive PKA contains two identical catalytic subunits (C) and two identical regulatory subunits (R).
4. Binding of two cAMP molecules to each PKA regulatory subunit. Regulatory subunits move out of the active site of catalytic subunit and R2C2 complex dissociates.
5. PKA is active when phosphorylated and can begin process of mobilizing glycogen stored in muscle and liver in anticipation of need of energy as signaled by epinephrine.

PKG:

1. Protein kinase G is a serine/threonine specific protein kinase that is activated by cGMP.
2. PKG is also known as cGMP dependent protein kinase.
3. The catalytic and regulatory domain of this enzyme are in a single polypeptide.
4. Binding of cGMP forces the pseudo-substrate out of the binding site to target protein containing PKG consensus sequences.
5. PKG activity modulates several targets involved in muscular contraction.