Intracellular and Extracellular Metabolism of Adenosine and Adenine Nucleotides

ATP is not solely the major intracellular biochemical energy currency, directly regulating the activities of a wide variety of proteins and other molecules which are substrates for phosphorylation. It also serves as the precursor for an important intracellular second messenger molecule, cyclic AMP, which in turn regulates the activities of a subset of proteins via cyclic AMP-dependent protein kinases, as discussed elsewhere in this volume.