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Xenobiotics
are chemical compounds that do not belong to the normal
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composition
of the human body. These compounds enter the body via
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the
diet, air and medication. The principal route of elimination of
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xenobiotics
from the body is biotransformation. They are eliminated by
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microsomal
phase I and microsomal and cytosolic phase II
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drugmetabolising
enzymes. These enzymes add functional groups to
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make
lipophilic molecules more hydrophilic and hence easier to
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eliminate.
The oxidative reactions are mainly catalysed by cytochrome
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P450
(CYP or P450) enzymes. The CYP superfamily of microsomal
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hemoproteins
catalyses the monooxygenation of a large number of
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endogenous
and exogenous compounds. They play a key role in the
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metabolism of a wide variety of
xenobiotics, such as drugs, pesticides
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and
(pre)carcinogens.
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