Manganese is an essential trace nutrient in all forms of life.
Most organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide. The human body contains about 10 mg of manganese, which is stored mainly in the liver and kidneys. The classes of enzymes that have manganese cofactors include oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The best known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).
Mn-SOD is the type of SOD present in eukaryotic mitochondria, and also in most bacteria. Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants (photosynthesis). Most broad-spectrum plant fertilizers contain manganese.
Though adequate amounts are helpful, too much can be toxic to the brain and nerves.