Molybdenum biological function

A molybdenum-binding ionophore has been described, namely a peptide secreted by Bacillus thuringiensis which can bind MoO ion. Its biological function is not known.81 Curiously the secretion of this peptide appears to occur under conditions of iron depletion. 

It is interesting to speculate on the chemical properties of molybdenum which make it suitable for its biological function. Obvious features in the chemistry of molybdenum are (a) a range of oxidation states which can be stabilized in aqueous solution by the common ligands of biology (b) the formation of oxo compounds and the sulfur analogue (c) the ability to participate in atom-transfer reactions and (d) the possibility of higher coordination numbers. 

Cohen, H.J., R.T.Drew, J.L.Johnson, and K.V.Rajagopalan. 1973. Molecular basis of die biological function of molybdenum The relationship between sulfite oxidase and the acute toxicity of bisulfite and S02. Proc. Natl. Acad. Sci. 70(12) 3655-3659. 

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. 

Among the members of the second transition series, molybdenum is the only element definitely known to have specific biological functions. With an atomic weight of... 

Transition elements have some biological functions for chemistry of living systems. Metals, such as iron, cobalt, copper, and molybdenum have functions in living systems, whereas protein contains iron, which helps in electron transfer and oxygen transport. Most transition metal elements plays similar major roles in various biological living systems and for these reasons we focused on the transition metals. 

Vanadium, like molybdenum, has two very different catalytic activities associated with it and two very different biological functions. Both elements... 

The first indication of an essential metabolic role for molybdenum was obtained in 1953, when it was discovered that xanthine oxidase, important in purine metabolism, was a metalloenzyme containing molybdenum. Subsequently the element was shown to be a component of two other enzymes, aldehyde oxidase and sulphite oxidase. The biological functions of molybdenum, apart from its reactions with copper (see p. 123), are concerned with the formation and activities of these three enzymes. In addition to being a component of xanthine oxidase, molybdenum participates in the reaction of the enzyme with cytochrome C and also facilitates the reduction of cytochrome C by aldehyde oxidase. 

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

Many of the most important catalytic activities of coordination compounds and metal ions (particularly iron and copper) are in the electron transport chains of cellular metabolism, where they act as catalysts for the oxidation of organic intermediates. Several other transition metal ions (including vanadium and molybdenum) have important metabolic roles in a variety of organisms. Indeed, recent discoveries suggest that even such metals as chromium and nickel have biological functions. 

The quality of the experimental evidence for nutritional essentiality varies widely for the ultratrace elements. The evidence for the essentiality of three elements, iodine, molybdenum and selenium, is substantial and noncontroversial specific biochemical functions have been defined for these elements. The nutritional importance of iodine and selenium are such that they have separate entries in this encyclopedia. Molybdenum, however, is given very little nutritional attention, apparently because a deficiency of this element has not been unequivocally identified in humans other than individuals nourished by total parenteral nutrition or with genetic defects causing disturbances in metabolic pathways involving this element. Specific biochemical functions have not been defined for the other 15 ultratrace elements listed above. Thus, their essentiality is based on circumstantial evidence, which most often is that a dietary deprivation in an animal model results in a suboptimal biological function that is preventable or reversible by an intake of physiological amounts of the element in question. Often the circumstantial evidence includes an identified essential function in a lower form of life, and biochemical actions consistent with a biological role or beneficial action in humans. The circumstantial evidence for essentiality is substantial for arsenic, boron, chromium, nickel, silicon, and vanadium. The evidence for essentiality for the... 

None of the suggested biological functions or roles of any of the ultratrace elements have been conclusively or unequivocally identified in higher forms of life except for those of molybdenum. 

Bi-functional radio-analytical scheme, based on exchange and extraction column chromatography, which provides the reliable information on molybdenum and uranium contents in biological materials has been elaborated. The contribution of uranium fission reaction has been strictly monitored. The uncertainty of the results of Mo determination by the presented method is very low. 

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