Citreoviridin is a mycotoxin isolated from several Penicillium species that has been shown to inhibit the mitochondrial ATP synthetase system. It inhibits soluble ATPase (KD = 4.1 μM), ADP stimulated respiration in isolated rat liver mitochondria (KD = 0.15 μM), and ATP-driven reduction of NAD+ by succinate (KD = 2 μM). Citreoviridin has been used to target ectopic ATPase activity in cancer cells in order to modulate the metabolic activity associated with tumorigenesis.