Protein kinase A

Protein Kinase A (PKA) is a protein that is dependent on cyclic AMP (cAMP) and without it, is deactivated. PKA is involved in signal-transduction pathways and phosphorylates proteins by adding a phosphate group. The molecule consists of two subunits, a regulatory subunit and a calalytic subunit . These subunits are inactive when cAMP is not bound. When cAMP binds to a regulatory subunit a conformational change occurs. This change means that the catalytic subunit becomes active and is no longer inhibited. This means that the protein can now phosphorylate other proteins by removing a phosphate from ATP, and adding it to a serine residue on the target protein which in turn leads to a cellular response.