NQO1 plays a role in ubiquinone and vitamin E quinone metabolism. The mobile electron carriers are, as usual, a lipid-soluble quinone and a water-soluble cytochrome. Subsequent oxidation of the hydroquinone gives the quinone. Not all inhibitors are radicals however, with quinones and quinone methides being important examples. Pyrroloquinoline quinone (PQQ), also called methoxatin"," is a redox cofactor. I are primarily driven by the quinone redox cycle. It is a planar molecule with one aromatic ring fused to a quinone subunit. These changes in redox potential are caused by changes in structure of quinone. It is more electrophilic than quinone itself. Quinhydrone is a cocrystal of quinone and hydroquinone (known archaically as quinol). Toxicity of paracetamol is believed to be due to its quinone metabolite NAPQI. Urushiols are oxidized in-vivo, generating a quinone form of the molecules. It may also increase quinone type free radical production, hence contributing to its cytotoxicity. PPO-silenced apples are unable to convert chlorogenic acid into the standard quinone product. In strongly basic media and the presence of air, it is oxidized to a quinone.