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BIOLOGICAL ELECTRON TRANSFER SEQUENCES
~~~ lecture notes by Thomas L. Hesselink, MD ~~~
5th Edition, Copyright 2002
This lecture reviews the metabolism of reducing equivalents
(electrons and hydrogen atoms).
All living things depend upon the orderly transfer of reducing
equivalents from food/fuel molecules to some final electron
acceptor. In "aerobic" organisms diatomic oxygen is most
frequently utilized as the final electron acceptor. However,
under special circumstances, hydrogen peroxide or pyruvate
can also be used. In "anaerobic" organisms weaker oxidants
such as sulfate, carbon dioxide, nitrate, or pyruvate are
used as final electron acceptors.
In living things some transfers of electrons and hydrogen
atoms take place as simple two reactant oxidation-reductions,
such as occur in a test tube or battery. However, most
transfers occur in multi-step sequences which are carefully
regulated. Thus reducing equivalents pass from one carrier
in the sequence to the next, much like buckets along a bucket
brigade or batons in a relay race. Their movement is governed
by: reactant concentrations, relative redox potentials, pH,
and enzymatic facilitation. These delicate systems can be
blocked by respiratory poisons such as: mercury II, ammonia,
cyanide, or sulfide. They can also fail due to nutritional
deficiency of key components such as: riboflavin, copper,
selenium, ascorbate, bioflavonoid, or cysteine.
Diseases such as allergies, infections, and cancers are
associated with some focus of failure in a biological
electron transfer sequence. This failure allows an excess
of reductant materials of various types to accumulate and
support the disease process. Therapeutic oxidants accelerate
the removal of these reductants. When successful, the
therapeutic oxidant administered consumes enough reductant
material such that the pathologic process cannot persist.
Medicinal oxidants need not abstract electrons or hydrogen
atoms directly from the site of pathology. Instead the
process can be quite indirect. In other words the medicinal
oxidant can abstract reducing equivalents from any of several
ambient hydrogen/electron carriers. As these oxidized carriers
get physiologically recharged, electrons or hydrogen atoms
are drawn away from other sites. This includes the pathologic
site. A considerable variety of oxidants can induce this
redistribution of reducing equivalents. This explains why
so many different oxidizing agents have been found to produce
similar therapeutic benefits.
Also medicinal oxidants can produce numerous physiologic
effects. These include: enhanced release of oxygen from
oxyhemoglobin, stimulated release of immunoactive cytokines,
antioxidant adaptation, and initiation of programmed cell
death in certain cells.
This lecture introduces the most common types of electron
carriers and hydrogen carriers found in living things.
It explains the molecular mechanisms whereby each can be
oxidized and reduced reversibly. Several types of biological
electron transfer sequences (BETS) are illustrated, and
their are functions identified. How medicinal oxidants alter
the flow and distribution of reductants along the myriad
BETS is explained. As these alterations take place the
benefits of the medicinal oxidant begin to manifest.
Thus the biochemical mechanisms underlying the oxidative
therapies will become apparent.