Copper is required for the functioning of many enzymes, such as cytochrome c oxidase, which is complex IV in the mitochondrial electron transport chain, ceruloplasmin, Cu/Zn superoxide dismutase, and in amine oxidases. These enzyme catalyze reactions for oxidative phosphorylation, iron transportation, antioxidant and free radical scavenging and neutralization, and neurotransmitter synthesis, respectively. Diets vary in the amount of copper they contain, but may provide about 5 mg/day, of which only 20-50% is absorbed. The diet of the elderly may have a lower copper content than the recommended daily intake. Dietary copper can be found in whole grain cereals, legumes, oysters, organ meats (particularly liver), cherries, dark chocolate, fruits, leafy green vegetables, nuts, poultry, prunes, and soybeans products like tofu.