Farr effect:
The profound increase in oxygen absorption via the pulmonary
route, which occurs in vivo during intravenous infusion
of a dilute solution of hydrogen peroxide. This was discovered
by Charles Farr, M.D., Ph.D. while researching the physiologic
effects of hydrogen peroxide.
Fenton reaction:
the reduction of hydrogen peroxide (HOOH) by ferrous cation
(Fe++) producing hydroxyl radical (HO*) and hydroxide anion (OH-).
flavin:
a tricyclic compound containing an aromatic ring, a heterocyclic
ring, and a lactam ring usually connected to a sugar molecule;
the redox active center of flavoproteins; the yellow colored nonribose
part of riboflavin (vitamin B2). Flavin is a conjugated diimine which
is able to reversibly accept one or two hydrogen atoms at a time.
Its highly conjugated structure provides stability to its semireduced
radicalized form. It is ubiquitous in living things as an essential
cofactor to numerous oxidoreductases and oxygenases.
flavin-adenine-dinucleotide (FAD):
an essential cofactor to numerous
oxidoreductases composed of a flavin molecule and an adenine molecule
covalently linked by a glycoside bridge. FAD is tightly bound to the
apoenzyme that it activates. Its reduced form is symbolized by FADH2.
flavoprotein:
any enzyme (usually an oxidoreductase) utilizing flavin as
a cofactor (usually FAD or FMN).
ferric cation (Fe+++):
the more fully oxidized and trivalent form of iron. Fe+++ is
a medium strength oxidant. It is poorly soluble in water due to its
tendency to form precipitates with numerous anions. It can be suspended
or solubilized by various chelators or carrier proteins. Ferric compounds
are usually red to brown in color. Numerous oxidoreductases utilize Fe+++
in their active centers due to its facile and reversible conversion
by one electron reduction to ferrous cation (Fe++).
ferrous cation (Fe++):
the partially oxidized divalent form of iron. It is
a weak oxidant and a weak reductant. It is more readily soluble in water
and binds less tightly to chelators and carrier proteins than Fe+++.
It is yellowish green in color. Numerous oxidoreductases utilize Fe++
in their active centers due to its facile and reversible conversion by
one electron oxidation to Fe+++. Examples include: iron-sulfur centers,
cytochromes, and peroxidases. Hemoglobin and myoglobin utilize ferrous
iron not as a reductant but as a carrier of diatomic oxygen. Fe++ can
reduce numerous compounds of oxygen to either generate or to quench
oxyradicals depending on circumstances.
folic acid:
a B vitamin essential to numerous metabolic pathways which
metabolize methyl and other single carbon groups. Folic acid must be
enzymatically reduced by the addition of four hydrogen atoms supplied
by NADPH to become active.
free radical (R*):
a limb or ray of a larger molecule considered to have
been broken off by physical or chemical action; any compound containing
one or more unpaired electrons. These are highly reactive compounds and
are usually very short lived and unstable due to the unpaired electron
occupying a molecular orbital capable of holding two spin paired
electrons. Free radicals which involve oxygen atoms as the carrier of
the unpaired electrons usually behave as strong oxidants and readily form
electrophilic adducts to susceptible molecules.
