Excess copper is sequestered within hepatocyte lysosomes, where it is complexed with metallothionein. Copper hepatotoxicity is believed to occur when the lysosomes become saturated and copper accumulates in the nucleus, causing nuclear damage. This damage is possibly a result of oxidative damage, including lipid peroxidation. Copper inhibits the sulfhydryl group enzymes such as glucose-6-phosphate 1-dehydrogenase, glutathione reductase, and paraoxonases, which protect the cell from free oxygen radicals. It also influences gene expression and is a co-factor for oxidative enzymes such as cytochrome C oxidase and lysyl oxidase. In addition, the oxidative stress induced by copper is thought to activate acid sphingomyelinase, which lead to the production of ceramide, an apoptotic signal, as well as cause hemolytic anemia. Copper-induced emesis results from stimulation of the vagus nerve. Organic nitriles decompose into cyanide ions both in vivo and in vitro. Consequently the primary mechanism of toxicity for organic nitriles is their production of toxic cyanide ions or hydrogen cyanide. Cyanide is an inhibitor of cytochrome c oxidase in the fourth complex of the electron transport chain (found in the membrane of the mitochondria of eukaryotic cells). It complexes with the ferric iron atom in this enzyme. The binding of cyanide to this cytochrome prevents transport of electrons from cytochrome c oxidase to oxygen. As a result, the electron transport chain is disrupted and the cell can no longer aerobically produce ATP for energy. Tissues that mainly depend on aerobic respiration, such as the central nervous system and the heart, are particularly affected. Cyanide is also known produce some of its toxic effects by binding to catalase, glutathione peroxidase, methemoglobin, hydroxocobalamin, phosphatase, tyrosinase, ascorbic acid oxidase, xanthine oxidase, succinic dehydrogenase, and Cu/Zn superoxide dismutase. Cyanide binds to the ferric ion of methemoglobin to form inactive cyanmethemoglobin. (L97, L277, T49, A174, L280)