TABLE 4.3 Micronutrients (trace elements) needed by living organismsa
| Element | Cellular Function |
| Chromium (Cr) | Required by mammals for glucose metabolism; no known microbial requirement |
| Cobalt (Co) | Vitamin B12; transcarboxylase (propionic acid bacteria) |
| Copper (Cu) | Certain proteins, notably those involved in respiration, for example, cytochrome c oxidase; or in photosynthesis, for example, plastocynanin; some speroxide dismutases |
| Manganese (Mn) | Activator on many enzymes; present in certain superoxide dismutases and in the water-splitting enzyme of photosystem II in oxygenic phototrophs |
| Molybdenum (Mo) | Present in various flavin-containing enzymes; also in mylybdenum nitrogenase, nitrate reductase, sulfite oxidase; DMSO-TMAO reductases, some formate dehydrogenases; oxotransferases |
| Nickel (Ni) | Most hydrogenases; coenzyme F430 of methanogens; carbon monoxide dehydrogenase; urease |
| Selenium (Se) | Formate dehydrogenase; some hydrogenases; the amino acid selenocysteine |
| Tungsten (W) | Some formate dehydrogenases; oxotranserases of hyperthermophiles (for example, aldehyde: ferredoxin oxidoreductase of Pyrococcus furiosus) |
| Vanadium (V) | Vanadium nitrogenase; bromoperoxidase |
| Zinc (Zn) | Present in the enzymes carbonic anhydrase, alcohol dehydrogenase, RNA and DNA polymerases, and many DNA-binding proteins |
| Iron (Fe)b | Cytochromes, catalases, peroxidases, iron-sulfur proteins (for example, ferredoxin), oxygenases, all nitrogenases |
aNot every micronutrient listed is required by all cells; some metals are found in enzymes present in only specific microorganisms.
bNeeded in greater amounts than other metals-not generally considered a trace element.