Figure 1.

Extracellular and intracellular adenosine pathways. CD73, a 5′-ectonucleotidase, is a rate controlling enzyme of the extracellular ADO pathway. CD73, as soluble or exosomal 5′–nucleotidase, also produces intracellular ADO from AMP. ADO signals via four P1 purinergic receptors expressed on a wide variety of cell types. The figure is modified and reproduced with permission from ref. 17.