Tungsten biological function

Molybdenum is very important in the biochemistry of animals, plants, and microorganisms. It is the only element in the second transition series known to have natural biological functions. It occurs in more than 30 enzymes, in some of which it may be replaced by tungsten or vanadium. Tungsten is the only element in the third transition series known to have natural biological functions. Not only does it sometimes occur in enzymes that usually contain molybdenum, but there are some enzymes that are known only with tungsten. 

Molecular basis of the biological function of molybdenum Molybdenum-free xanthine oxidase from liver of tungsten-treated rats, J. Biol. Chem. 249 5056 (1974). 

There were 37 distinct enzymes that contain molybdenum or tungsten known by the end of 1997. The enzymes are diverse in function, broadly distributed, and include oxidases, reductases, dehydrogenases, a transhydroxylase, and a hydratase. The Mo enzymes are found in eubacteria, archae, protista, fungi, plants, and animals (including humans) and are essential for respiration and carbon and nitrogen assimilation. Several of the enzymatic substrates and products are key components in the nitrogen, sulfur, selenium, carbon, and arsenic cycles and have major biological and environmental impact. 

There are only a few reports in which XAS has been applied to the archaeal tungsten enzymes, but nevertheless the technique has proved important. Just as molybdenum is the only second-transition element to have a function in biology, tungsten is the only third-transition element and also the heaviest element that is known to have a function in biology. Tungsten has a very similar chemistry to molybdenum and a detailed review of the comparative chemistry of the two elements has recently been reported. " The redox couples relating the... 

---