Arsenic biological roles

No biological role has been demonstrated for mercury, other than its interaction with essential nutrients and toxicity (Natl. Research Council, 1978). Moderate growth stimulation by low dietary levels of cadmium has been described by Schwarz (1977) but not independently confirmed. Therefore, the following discussion will be limited to two trace elements, arsenic and lead, until recently known only for their toxicity. Arsenic deficiency has been produced in goats, minipigs, rats and chicken (Anke et al., 1976 Nielsen and Schuler, 1978 Uthus and... 

Modem experiments with animals have shown that arsenic has a positive biological role, probably for protein synthesis. It is thus an essential element for some animals, perhaps also for humans. A low necessary intake, 0.1 mg per day, is obtained from drinking water. 

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... 

Andreae, M. O. (1979). Arsenic speciation in seawater and interstitial waters the role of biological-chemical interactions on the chemistry of a trace element. Limnol. Oceanog. 24,440-452. 

HOCl is one of the oxidants that activated phagocytes have in their arsenal. Hu et al. (1993) have shown that plasma albumin sulphydryl and ascorbic acid both protect against oxidant injury from HOCl. Neutrophils, interestingly, contain about 25 times more ascorbic acid than plasma. This su ests an endogenous self-protection role. This work is important because of the biological emphasis of reactive chlorine by the neutrophil. 

Marafante, E., Vahter, M. and Envall, J. (1985) The role of the methylation in the detoxication of arsenate in the rabbit. Chemico-Biological Interactions, 56(2-3), 225-38. 

Techniques and approaches to the study of the distribution of chemical species of metals and metalloids in biological materials after sample preparation are similar to those already described for other matrices in this book, and in a recent review by Lobinski (1997). The application of these methods has led to a greater understanding of the role of metals and metalloids in biological systems. Some of the new developments in understanding the environmental behaviour of antimony, arsenic, selenium and tin are reviewed. 

It is well known that pentacovalent cyclic phosphorus compounds play an important role as intermediates in reactions involving nucleophilic attack on tetracoordinated phosphorus in biological systems. According to this background it appears to us that it is important to prepare the arsenic derivatives, which are more stable than the corresponding phosphorus compounds and allow the study of their conformation. 

The enzymology of arsenic biomethylation is complicated because of its many oxidation states, its propensity to react with sulfur compounds, and low concentrations of arsenic compounds in biological specimens. The chemical intermediates and reactions in the metabolism of arsenate are similar in microorganisms and animals. However, in microorganisms, the reactions tend to proceed to methylarsines, whereas in mammalian species the major urinary metabolite is generally dimethylarsinate and only a very small amount of it is reduced further. The arsenate reductase and methylarsonate reductase were thought to play an important role in arsenic biomethylation however, with the exception of arsenate reductase most of the enzymatic experiments involved mammalian systems. 

Chapter 6 describes the chemistry of arsenic, antimony, and bismuth, including a discussion of the role that these elements play in the environment and biology and medicine. Applications of these complexes are also discussed. 

The heavy metal in the environment collocation refers to any metallic chemical element and some metalloids (e.g. arsenic) that are toxic or poisonous for living organisms even at low concentration, e.g. Pb, Cd, Hg, As, H, Cr. They originate in the Earth s crust as well as in the majority of wastes resulting from anthropogenic activities. Toxic effects of other heavy metals (Cr, Mo, Ni, As, Se etc.) have to be considered separately from the effects of biologic doses in which they exert their vital role. 

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