Catalyzes the reversible transfer of the terminal phosphate group between ATP and AMP (PubMed:15478799). Has very low activity with CTP, GTP, ITP and UTP and no activity with GMP, CMP, UMP or IMP in vitro (PubMed:15478799). AMP + ATP = 2 ADP Inhibited by the dinucleoside pentaphosphate compound P1,P5-di(adenosine-5') pentaphosphate (AP5A). kcat is 35 sec(-1) (at 25 degrees Celsius and pH 6). Optimum pH is 5.5. Belongs to the adenylate kinase family.