Mechanisms of Action
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Mercury is found in liquid form at room temperature, but it has a very high vapour pressure, which causes it to be more toxic that it would be otherwise.
In its gaseous state, mercury, Hg(g), is highly toxic. This is because it dissolves very easily in lipids, and is absorbed very easily by red blood cells and nerve cells, due to the following reactions.
R-SH + Hg(II) ----> R-S-Hg The elemental mercury, Hg(0) is transformed to Hg(II), which is much more toxic because it bonds easily with the sulphhydryl groups found on enzymes. A lot of cell injury results from mercury’s ability to bind with enzymes, and, since mercury has a tendency to attack the central nervous system more than other parts of the body, the organism or victim exposed to mercury usually experiences seizures or tremors. The bodies of most organisms, however, are able to deal with very, very low quantities of mercury. When the kidney is exposed to small amounts of mercury, it starts to produce chemicals called ‘metallothioneins’, which is actually a combination of two proteins with sulphhydryl groups; its purpose is to metabolise and regulate metals. In the human body, large quantities are synthesised primarily in the liver and kidneys. Its production is dependent on availability of the dietary minerals zinc and selenium, and the amino acids histidine and cysteine.  Instead of attacking other enzymes, the mercury binds with the metallothionein, and eventually leaves the system through excretion. Thimerosal causes susceptible bacteria to autolyze (break down their own cells with self-produced enzymes) via an unknown mechanism. In the body, it is metabolized or degraded to ethylmercury (C2H5Hg+) and thiosalicylate. It is suspected that, from here, the ethyl mercury, the greater toxicant, reacts with the sulphydryl groups on enzymes. The sodium binds back with the thiosalicylate, and, eventually, passes through the body.
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