decarboxylase:
an enzyme which eliminates the carboxyl group from an organic
acid and substitutes a hydrogen atom, in the process releasing one
molecule of carbon dioxide. Some decarboxylases convert amino acids to
primary amines.
deferoxamine:
a chelating agent especially suited to binding trivalent
cations such as ferric (Fe+++) or aluminum (Al+++).
dehydroascorbic acid (DHAA):
the oxidized form of vitamin C; ascorbic acid
from which two hydrogens have been removed.
dehydrogenation:
the abstraction of hydrogen; oxidation by the removal of
hydrogen; conversion of a saturated organic molecule to unsaturated.
dehydrogenase:
any of several families of enzymes which serve to abstract
hydrogen from specific substrates; an oxidoreductase emphasizing its
oxidizing action along the particular metabolic pathway that it serves.
Dehydrogenases transfer hydrogen from various fuel molecules and pass it
on the various hydrogen carriers such as NADH, NADPH, FADH2, CoQH2, etc.
dehydroepiandrosterone (DHEA):
a steroid hormone and precursor to the sex
steroids. DHEA has numerous metabolic functions, among them being the
inhibition of glucose-6-phosphate dehydrogenase and the induction of
glycerol phosphate dehydrogenase.
deiodination:
the process of removing an atom of iodine from an organic
iodide and substituting an atom of hydrogen. Deiodination converts
thyroxine (T4) to liothyronine(T3).
deoxyribonucleoside-5'-diphosphate (dNDP):
a three part molecule consisting
of a nitrogenous base (adenine, guanine, cytosine, or uracil) covalently
bound to the 1' carbon of deoxyribose, plus a pyrophosphate group
(a diphosphate) esterified to the 5' carbon of deoxyribose; the product
of ribonucleoside reductase (RR). After further modifications the dNDP's
become precursors to DNA synthesis.
detoxification (detox):
any biochemical process by which toxins or excess
metabolites can be removed from the organism. Some steps in these
processes may under certain conditions cause a given substance to become
more toxic. Certain detox functions can be supported nutritionally
or be induced by certain herbs or drugs.
diacetyl (CH3-CO-CO-CH3):
dimethyl glyoxal; 2,3-dioxo-n-butane; biacetyl.
Diacetyl is the substance which gives flavor to butter. Under certain
biological conditions it can act as a hydrogen acceptor.
diamide ((CH3)2-N-CO-N=N-CO-N-(CH3)2):
diazenedicarboxylic acid bis (N,N-dimethylamide),
an oxidant probe for thiols. Diamide dehydrogenates
thiols by a two step nucleophilic mechanism.
diamine oxidase (DAO):
histaminase; any of a family of enzymes which catalyses
the oxidation of diamines such as histamine, putrescine,
or the polyamines. The substrates are converted to an
aldehyde and ammonia. DAO is especially abundant in bovine
serum and has inhibited the growth of certain microorganisms
when bovine blood was tried as a growth medium. DAO is found
in high concentration in human enteral cells where it oxidizes
various diamines produced in the bowel by putrifaction. DAO
is released into human plasma upon administration of heparin.
DAO utilizes copper and trihydroxyphenylalanine quinone (TPQ)
as cofactors.
diatomic oxygen (O2 or *OO*):
regular atmospheric oxygen; oxygen in its
lowest energy state which is a diradical and a triplet; any species of
oxygen containing only two atoms of oxygen.
dicarbonyl compound:
any organic compound which contains two carbonyl groups.
Of special interest in biooxidative medicine are those in which the
carbonyl groups are conjugated which enables them to redox cycle under
biological conditions.
dihydroflavin (FADH2):
leukoflavin; the reduced form of flavin-adenine-
dinucleotide. Many dehydrogenases and reductases utilize FAD in the
active center. FADH2 represents the reduced phase which serves as a
hydrogen donor. Depending on the particular enzyme and other
circumstances involved, FADH2 will reduce pyridiniums, disulfides,
quinones, or diatomic oxygen.
dihydroxyacetone phosphate
(DHAP or CH2OH-CO-CH2-OPO3--):
the oxidized phase of an important hydrogen shuttle for the mitochondria.
DHAP is produced upon dehydrogenation of glycerol-3-phosphate.
dimercaptopropane sulfonate (DMPS):
a chelating agent having two thiol groups and an especially potent
agent for binding mercury II (Hg++) cations.
dimercaptosuccinic acid (DMSA or COOH-HCSH-HCSH-COOH):
a chelating agent having two thiol groups and especially
useful medicinally to bind lead or mercury.
dimerization:
the process of two molecules becoming bound together usually
covalently.
dimethyl sulfoxide (DMSO or CH3-SO-CH3):
a compound composed of a central
atom of sulfur bound to one atom of oxygen and two methyl groups.
DMSO is a liquid at room temperature and a highly versatile solvent
able to dissolve polar and nonpolar molecules. It causes tissues to
become more permeable to numerous substances. It can be reduced by
thiols to become the foul smelling dimethyl sulfide (DMS or CH3-S-CH3).
DMSO is a highly effective quencher of hydroxyl radical (HO*),
but is fairly inert towards superoxide radical (-OO*).
dioxetane:
a four membered heterocyclic ring composed of two atoms of carbon
and two atoms of oxygen in the order CCOO. Dioxetanes are produced by
the direct addition of singlet oxygen (energized diatomic oxygen) to
an olefin. Dioxetanes are unstable and decompose to become two seperate
carbonyl compounds, usually aldehydes.
dioxygenase:
an enzyme which serves to catalyze the addition of two atoms
of oxygen to the substrate.
diphenoquinone (O=C(-C=C-)2C=C(-C=C-)2C=O):
an extended quinone composed of two rings of six carbon atoms
each of which has a carbonyl group and two conjugated ethylene
linkages, the rings being linked by a carbon to carbon double
bond. Diphenoquinones can be produced by the oxidative coupling
of phenols. They react similarly to other quinones such as
benzoquinones.
2,3-diphosphoglycerate (2,3-DPG):
a metabolite of glycolysis which is
produced in greater quantity as a secondary response to glutathione
oxidation. 2,3-DPG binds reversibly to hemoglobin and causes it to more
readily release oxygen to peripheral tissues.
dipole:
a molecule which possesses distinct positive and negative parts.
Such compounds are more soluble in polar solvents such as water, than are
nonpolar molecules such as lipids. Molecules containing dipoles readily
form loosely bound complexes with ions.
dismutation:
the disproportionation of superoxide to produce hydrogen
peroxide and diatomic oxygen.
disproportionation:
the process by which like molecules transfer reducing
equivalents between each other; self oxidation-reduction.
disulfide (RSSR'):
any molecule containing a bridge composed of two sulfur
atoms. Disulfides can be reduced by the donation of two hydrogen atoms
to become two separate thiols. Disulfides can be produced by the oxidation
of thiols (RSH) to thyil radicals (RS*) which subsequently couple.
dithiothreitol (DTT or CH2SH-CHOH-CHOH-CH2SH):
1,4-dimercapto-2,3-dihydroxy-
n-butane; a four carbon chain with two redox active thiol groups at the
ends useful as a research tool to study the effects of adding a reductant
to the test medium. Many enzymes requiring thiol groups to be active
are reversibly inhibited by oxidation to disulfides. These can be
reactivated upon contact with DTT.
divalent:
1) existing in two oxidation states. Sodium, for example, can exist
as a metal and as a cation of one unit positive charge.
2) the two plus oxidation state of a metal or other positively charged
molecular species baring two units of charge per molecule.
docosoid:
any of several families of physiologic regulators which are lipids
having twenty carbon atoms. Examples are: prostaglandins, thromboxanes,
and leukotrienes.
double bond:
a covalent bond consisting of one sigma bond accompanied by
one pi bond. This orbital configuration prevents rotation. In structural
formulas the double bond is usually depicted as two parallel linear
segments between atoms, but the actual spacial form is more like three
parallel segments the middle representing the sigma bond and the two
outer segments representing the pi bond. The pi bond is the more
reactive of the two.
