Arsenic function

Arsenate, As04 , is an uncoupling reagent for oxidative phosphorylation, but unlike DNP it does not transport protons across the inner mitochondrial membrane. How might arsenate function as an uncoupler ... 

Several of the approaches to fully conjugated systems are also applicable to the synthesis of arsenic-containing dihydro derivatives. Of these, 3-arsolenes are common, whereas the only 2-arsolene synthesis occurs by isomerization. Benzo derivatives are also known. These methods allow preparation of compounds of different arsenic functionality (e.g., As-Cl, /fs-alkyl, 45-aryl), so different systems may be prepared by interconversion from one type of functionality to another. Stibolenes and bismolenes are still unknown. 

Between the summer of 1940 and the declaration of war, two changes were effected at CWS installations. In August 1940 Fort Hoyle, a Field Artillery installation adjacent to Edgewood Arsenal, was vacated and the land and buildings turned over to the CWS. This space was sorely needed in the period of expansion. In December 1940 an arsenal operations department was set up at Edgewood to supervise strictly arsenal functions such as production, service, and inspection. 

It was proposed over 20 years ago that arsenate functions as an alternate substrate for the membrane-bound, proton-translocating ATP-synthetase. This enzyme was thought to catalyze the formation of ADP-arsenate which would hydrolyze rapidly (Avron, Jagendorf 1959). Only recently this has been confirmed in mitochondria (Moore, Gresser 1982) and R. rubrum chromato-phores (Slooten, Nuyten 1983). Aside from the coupled enz)mie assay used to trap ADP-arsenate (Moore, Gresser 1982), we demonstrate here two other methods for the measurement of the synthesis and hydrolysis of ADP-arsenate, and apply them to a determination of some kinetic constants for arsenylation and phosphorylation of ADP and GDP. 

In recent years, biochemists have developed an arsenal of reactions that are relatively specific to the side chains of particular amino acids. These reactions can be used to identify functional amino acids at the active sites of enzymes or to label proteins with appropriate reagents for further study. Cysteine residues in proteins, for example, react with one another to form disulfide species and also react with a number of reagents, including maleimides (typically A ethylmaleimide), as shown in Figure 4.11. Cysteines also react effectively... 

The effect of a particular element on the odour of its compound seems also to lend support to the residual affinity theory, for it is only the elements which possess residual affinity in certain of their compounds, which function as osmophores. Oxygen, nitrogen, sulphur, phosphorous, halogens, arsenic, antimony, bismuth, etc., whose valencies vary under certain conditions are powerfully osmophoric whereas carbon, hydrogen, and many others which have a constant valency are practically non-osmophoric, and it is very instructive to note that the element is osmophoric when it is not employing its full number of valencies and therefore has free affinity. 

USAARMCOM Regulation 10-10 assigns Pica-tinny Arsenal its mission, major functions and materiel assignments within the Armament Command. The following is an extract from that regulation ... 

Military Specification MIL-P-223B to Assure Functionally Reliable Black Powder , Picatinny Arsenal Report No ASRSD-QA-A-P-60 (June 1974), cited by Ref 110 80) J.E. Tanner, Jr,... 

Without known nutritional function but toxic in excess Aluminum, arsenic, antimony, boron, bromine, cadmium, cesium, germanium, lead, mercury, silver, strontium... 

For some toxins it is possible to demonstrate an apparent improvement in functional response at levels of exposure which are below a threshold. This effect, which has been termed hormesis , is most effectively demonstrated in the consistently improved longevity of animals whose caloric intake is restricted rather than allowing them to feed ad lib (Tannenbaum, 1942). Clearly in this instance, the observed effects are the result of exposure to a complex mixture of chemicals whose metabolism determines the total amount of energy available to the organism. But it is also possible to show similar effects when single chemicals such as alcohol (Maclure, 1993), or caffeic acid (Lutz et al., 1997) are administered, as well as for more toxic chemicals such as arsenic (Pisciotto and Graziano, 1980) or even tetrachloro-p-dibenzodioxin (TCDD) ( Huff et al., 1994) when administered at very low doses. It is possible that there are toxins that effect a modest, reversible disruption in homeostasis which results in an over-compensation, and that this is the mechanism of the beneficial effect observed. These effects would not be observed in the animal bioassays since to show them it would be necessary to have at least three dose groups below the NOAEL. In addition, the strain of animal used would have to have a very low incidence of disease to show any effect. 

Bennett MS, Z Guan, M Laurberg, X-D Su (2001) Bacillus subtilis arsenate reductase is structurally and functionally similar to low molecular weight protein tyrosine phosphatases. Proc Natl Acad Sci USA 98 13577-13582. 

The chlorate reductase has been characterized in strain GR-1 where it was found in the periplasm, is oxygen-sensitive, and contains molybdenum, and both [3Fe-4S] and [4Fe-4S] clusters (Kengen et al. 1999). The arsenate reductase from Chrysiogenes arsenatis contains Mo, Fe, and acid-labile S (Krafft and Macy 1998), and the reductase from Thauera selenatis that is specific for selenate, is located in the periplasmic space, and contains Mo, Fe, acid-labile S, and cytochrome b (Schroeder et al. 1997). In contrast, the membrane-bound selenate reductase from Enterobacter cloacae SLDla-1 that cannot function as an electron acceptor under anaerobic conditions contains Mo and Fe and is distinct from nitrate reductase (Ridley et al. 2006). 

Having said this, we like to view modem density functional theory as a very efficient additional tool in the arsenal of computational methods rather than a perfectly different... 

Tolerance in insects to increasing amounts of DDT, BHC, and several of the inorganic agents, such as arsenic, is known to occur. However, in animals, this phenomenon has not been demonstrated to the same degree. Ability of the cells of insects to function in the environment of a toxic agent, without alteration of cellular function, is one of the most striking of biologic phenomena. 

Heavy metals with no known biological function, such as aluminum, arsenic, lead, and mercury, are nonessential metals.4-5 These metals are toxic because they can irreversibly bind to enzymes that require metal cofactors. Toxic metals readily bind to sulfhydryl groups of proteins.6-7 In fact,... 

Fig. 8. Arsenic extraction from a reddish brown tropical soil deliberately contaminated with arsenate as a function of reaction time by 0.005M chloride, sulphate, carbonate and phosphate. Redrawn from Goh and Lym (2005).

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