Adenylate kinase (AK) regulates adenine nucleotide metabolism and catalyzes the ATP + AMP ⇌ 2ADP reaction in a wide range of organisms and bacteria. AKs regulate adenine nucleotide ratios in different intracellular compartments and maintain the homeostasis of the intracellular nucleotide metabolism necessary for growth, differentiation, and motility. To date, nine isozymes have been identified and their functions have been analyzed. Moreover, the dynamics of the intracellular energy metabolism, diseases caused by AK mutations, the relationship with carcinogenesis, and circadian rhythms have recently been reported. This article summarizes the current knowledge regarding the physiological roles of AK isozymes in different diseases. In particular, this review focused on the symptoms caused by mutated AK isozymes in humans and phenotypic changes arising from altered gene expression in animal models. The future analysis of intracellular, extracellular, and intercellular energy metabolism with a focus on AK will aid in a wide range of new therapeutic approaches for various diseases, including cancer, lifestyle-related diseases, and aging.

The balance between oxidative phosphorylation and glycolysis is important for cancer cell growth and survival, and changes in energy metabolism are an emerging therapeutic target. Adenylate kinase (AK) regulates adenine nucleotide metabolism, maintaining intracellular nucleotide metabolic homeostasis. In this study, we focused on AK3, the isozyme localized in the mitochondrial matrix that reversibly mediates the following reaction: Mg2+ GTP + AMP ⇌ Mg2+ GDP + ADP. Additionally, we analyzed AK3-knockout (KO) HeLa cells, which showed reduced proliferation and were detected at an increased number in the G1 phase. A metabolomic analysis showed decreased ATP; increased glycolytic metabolites such as glucose 6 phosphate (G6P), fructose 6 phosphate (F6P), and phosphoenolpyruvate (PEP); and decreased levels of tricarboxylic acid (TCA) cycle metabolites in AK3KO cells. An intracellular ATP evaluation of AK3KO HeLa cells transfected with ATeam plasmid, an ATP sensor, showed decreased whole cell levels. Levels of mitochondrial DNA (mtDNA), a complementary response to mitochondrial failure, were increased in AK3KO HeLa cells. Oxidative stress levels increased with changes in gene expression, evidenced as an increase in related enzymes such as superoxide dismutase 2 (SOD2) and SOD3. Phosphoenolpyruvate carboxykinase 2 (PCK2) expression and PEP levels increased, whereas PCK2 inhibition affected AK3KO HeLa cells more than wild-type (WT) cells. Therefore, we concluded that increased PCK2 expression may be complementary to increased GDP, which was found to be deficient through AK3KO. This study demonstrated the importance of AK3 in mitochondrial matrix energy metabolism.