The
Metabolism of
Selenium
The metabolism of selenium is well
– known, even though several characteristics make it
difficult to understand:
- this metalloid is
introduced in the human body with the help of aliments in different
chemical forms;
- chemically
speaking, selenium resembles sulphur very much, and therefore it will
sometimes be able to use the enzymatic or transport systems of the
latter.
The absorption of selenium depends on the form it is
found
in, and it is performed, at a faster or a slower rate, in the small
intestine. Selenites and selenates are absorbed first during the
intestinal digestion (in the duodenum), whereas the organic selenium
(selenium methitonine) is absorbed later (in the ileon, the site of the
small molecular chain peptides). The organic forms of selenium are
better absorbed than the inorganic (mineral) ones. The transport of
selenium in the plasma is nonspecific, selenium being usually bound to
a an b globulins and to albumin. Selenium is stored in the skeletal
muscles, in the liver and in the kidneys. It is eliminated in the urine
(60%), feces (35%), and very little through perspiration. The pulmonary
elimination of selenium is accompanied by a characteristic breath that
has the odor of garlic is always the sign of selenium excess
intoxication.
The
Biological Effects of
Selenium
The action
against free radicals. Selenium is a component of a human
protein,
formed of four identical subunits, each subunit including a selenium
atom in the form of selenium cysteine. This protein, containing
selenium, is part of the glutathione peroxidase structure, one of the
most efficient enzymes to fight free radicals excess. This discovery
was made in 1971 by Rotruck. Selenium cysteine is a selenium
–
amino acid in which selenium has taken the place of sulphur. The amino
acid that contains sulphur is called cysteine.
The seleno
–
aminic acids are a family of alpha – aminated acids , analogs
of
the metilcysteine, methionine, cysteine and cystathyonine, in which
sulphur has been replaced by selenium. They can be found in the plants
that grow on the selenipherous soils. They are antagonists of the
sulphur amino acids. In cattle seleno – aminic acids cause,
among
others, the specific manifestations of selenium poisoning. Selenium
cystationine causes various digestive disturbances. The main selenium
– aminic acids are: selenium – cystationine,
selenium
– cysteine, selenium – methyonine. In furry
animals, the
selenium acids excess causes “atrichia”, a genetic
disorder
characterized by absence of hair. By means of analogy, one can ask:
could selenium excess in the human body cause baldness?
Glutathione
peroxidase seems to be the only selenoenzyme known in the human body.
This enzyme is not only an important defending biomolecule, but also a
compensating system against the oxidative danger of intracellular
molecules, with small molecular masses: proteins, poliunsaturated fatty
acids. Neve, while studying the biological functions of selenium,
found in 1988 that the aggressions that occur during normal metabolic
processes or during some pathological circumstances ( inflammation,
arterial sclerosis, cancer, degenerative disorders, cellular ageing,
etc.) are connected to the free radicals and the dangers they carry
with them. Even the slightest selenium deficiency impairs the activity
of glutathione peroxidase and leads to the peroxidation of cellular and
intracellular membranes. The cellular permeability is disturbed, and
numerous biomolecules, such as DNA, continue to work, but due to those
anomalies the genetic code is changed. This is a risk, or at least a
plausible cause of cancer. The aggression caused by the selenium
deficiency causes specific clinical syndromes, such as: hemolysis,
tissue necrosis, degenerative disturbances, and, as a consequence, the
risk of chronic diseases increases.
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page ... → The
Role of Glutathione Peroxidase in the Metabolism of Prostaglandins
The
Disintoxication Action of SeleniumDecember
2, 2009
