Biological Electron Transfer Sequences


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 (O2) 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.