Catalyzes the reversible transfer of the terminal phosphate group between ATP and AMP. Plays an important role in cellular energy homeostasis, adenine nucleotide metabolism and plant growth. AMP + ATP = 2 ADP Monomer. Highly expressed in flowers and at lower levels in roots, leaves and stems. Enhanced root growth and increased amino acid biosynthetis in the light period. Belongs to the adenylate kinase family.