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Toxins That
Affect the Mitochondria
How might
mitochondria be affected by toxic chemicals? Mitochondrial
toxins fall into three categories. They can:
-
Inhibit electron transport. Interfere
with the transport of electrons through the chain of proteins
in the electron transport system (examples:
fungicides, some herbicides)
-
Uncouple phosphate bonding. Prevent
the creation of high energy phosphate bonds - without affecting
electron transport [ex: cyanide]
-
Have mixed action. Act
as in type 1 at high doses and act as in type 2 at low doses
(example: herbicides)
Electron
Transport Inhibitors
Environmental toxins such as
herbicides, insecticides, and fungicides can prevent the passing
of electrons by binding to one or more of the proteins that
carry electrons. Examples:
- Insecticide: (rotenone)
- Fungicides: (carfboxin, oxycarboxin, and
fenfuran)
- Herbicides: (chlorproham, propanil, dinoseb,
and ioxynil.)
Uncouplers
Cyanide is a well-known poison that
prevents the addition of high energy phosphate groups to make
the energy storage compound, ATP. Other well-known
compounds that act this way include the pesticides pentachlorophenl (PCP) and 2,4-dinitrophenol (DNP).
Mixed
Action Toxins
Certain herbicides inhibit
electron transport at high concentration and promote uncoupling at low concentrations. Some insecticides,
such as DDT and cyclodiene, are also in this group.
Something
to Think About
Part of the way that these toxins act comes
from their ability to penetrate and stick in membranes.
Recall that when any compound gets incorporated in a
membrane, as in our previous alcohol example, it can disturb the position of the other compounds that
are normally found there. In the membranes that make up the folds
inside of mitochondria, such disturbance interferes with the
passing of electrons that is needed to couple energy to ATP
synthesis.
Here is a question to think about: Could
herbicides and insecticides affect processes in other
membranes, such as those in the nuclear membrane or membranes
where proteins are made (endoplasmic reticulum), or even the
cell membranes of excitable cells such as nerve cells?
 
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