Fig. 1. Physiological role of AMPK in the cell. Catabolism `charges up the battery' by converting ADP to ATP (bottom curved arrow) whereas ATP-consuming processes convert ATP to ADP (top curved arrow). If a cellular stress causes the rate of catabolism to fail to keep pace with the rate of ATP consumption, ADP levels will rise and ATP levels will fall. ADP is converted into AMP by adenylate kinase and this, combined with the fall in ATP, will activate AMPK. AMPK then promotes the restoration of energy balance by stimulating catabolism and inhibiting ATP-consuming processes.