M
magnesium peroxide (MgO2):
a salt composed of the magnesium cation and the
dibasic peroxide anion. MgO2 has been used orally for broad spectrum
medicinal purposes. Upon reaction with water it slowly releases H2O2.
malic acid (COOH-CH2-CHOH-COOH):
hydroxysuccinic acid; the acid found in
apples and certain other fruit. Malate is part of the Kreb's cycle and
is dehydrogenated within mitochondria to produce NADH. Malic acid can
also enter the mitochondria from the cytoplasm so as to shuttle in
reducing equivalents.
malondialdehyde (MDA) (CHO-CH2-CHO):
malondialdehyde (MDA) (CHO-CH2-CHO):
a small 3 carbon molecule with a central methene group attached to
2 aldehyde groups. MDA is a breakdown product of lipid peroxides,
which were produced by peroxidation of polyunsaturated fatty acids.
manganese (Mn):
a multivalent transition metal. Cations of Mn can dismutate
superoxide an important protective role in mitochondria and in bacteria.
Mn activates several other types of enzymes.
mechanism:
the method or means by which molecules interact; the explanation
for how a chemical reaction takes place; the details pertaining
to how an enzyme functions.
menadione:
vitamin K3; 2-methyl-1,4-naphthoquinone; a synthetic form of
vitamin K and potent activator of prothrombin synthesis. Menadione has
demonstrated hydrogen shuttling, antiallergic, antibacterial, and
antineoplastic effects.
mercaptide (RSH):
a thiol; any organic compound with a thiol group. All such
compounds form strong ligand bonds with mercury II (Hg++).
2-mercaptoethanol (CH2SH-CH2OH):
a analogue of ethyl alcohol having a thiol
group at the alpha carbon atom. 2-mercaptoethanol is useful in research
as a test reductant. Many enzymes, which were converted to disulfides
by oxidants and thereby inhibited, can be reactivated by this compound.
mercapturic acid:
N-acetyl-L-cysteine-S-xenobiotic; the final excretory product
of xenobiotic conjugation with glutathione. Elevated urinary
mercapturates is a sign of excessive xenobiotic exposure
and suggests secondary glutathione depletion.
mercury (Hg):
a heavy metal which is oxidizable in vivo by peroxidases to
become mercury II (Hg++). Hg++ binds readily and tightly to virtually
all thiols/mercaptides. This characteristic makes Hg and most compounds
of Hg such as methyl mercury highly toxic at very low levels. Many
oxidoreductases require redox active thiols as part of their reactive
mechanism. Ligand binding to mercury can permanently inhibit these enzymes
at doses as low as one Hg++ cation per enzyme equivalent. Only other
thiols such as specialized chelators can reverse this inhibition.
metabolism:
the chemical activity of living things; a biochemical process;
the pathways by which certain substances are processed in vivo.
metabolite:
substances which are chemically produced by living things; any biochemical
product such as: a nutrient activation product, an intermediary product,
a waste product, or a detoxified xenobiotic.
metal toxicity:
enzymatic inhibition by attachment of metal cations to certain
electronegative ligands of the enzyme; or the production
of oxyradicals by redox cycling of metal cations as they
undergo single electron shifts of valence. The cations of
various heavy metals tend to bind tightly to thiol groups,
rendering them nonfunctional. Nitrogenous groups such as
amines and imines can similarly be disabled by toxic metals.
metallothionein (MT):
any of several proteins rich in cysteine and found in
most organisms studied. MT binds metal cations as a chelating agent or
carrier molecule. MT can bind up to seven cations per peptide. MT is
also induced in response to oxidative stress, its numerous thiol groups
serving as rechargeable reductive antioxidants. Oxidized MT forms mixed
disulfides with itself and with other thiols such as glutathione. MT is
released in response to inflammation and is responsible for a the
temporary decline in free zinc levels found in acute infections.
methylglyoxal (MG)(CH3-CO-CHO):
2-oxopropanal; pyruvic aldehyde; a three
carbon aldehyde with a keto group alpha to the aldehyde group. MG can be
rapidly cleared by the action of glyoxalase which converts it to lactic
acid. Reduced glutathione (GSH) is a cofactor required for glyoxalase to
function. Like certain other alpha-keto-aldehydes, MG is an
antiproliferative agent.
methylguanidine (CH3-NH-CNH-NH2):
a product of protein putrifaction involving the anaerobic
metabolism of arginine.
microaerophilic:
preferring to live and multiply in an environment of low
oxygen tension; able to live optimally with little oxygen.
microgram (mcg):
one millionth of a gram; 10 exp -6 gram.
mild silver protein:
an antiseptic/antibacterial colloid composed of small
amounts of silver cation (Ag+) bound to the ligands of various proteins.
milligram (mg):
one thousandth of a gram; 10 exp -3 gram.
mitochondrion / mitochondria:
a tiny intracellular organelle which possesses two membranes,
specialized enzymes, and its own DNA. Mitochondria serve several functions
including: oxidative deamination, the conversion of ammonia to urea,
the processing of numerous carboxylic acids to generate NADH and CO2,
the phosphorylation of ADP, and the absorbtion of reducing equivalents
from the cytosol by shuttles.
mixed function oxidase (MFO):
an enzyme complex which adds one atom of oxygen
to a wide variety of substrates or xenobiotics; phase one of xenobiotic
detoxification. MFO converts aromatic compounds into epoxides and phenols.
It consumes two reducing equivalents to convert one of the atoms of
diatomic oxygen to H2O, while delivering the other to the substrate.
Its several redox active components catalyze other reactions such as:
the reduction of quinones to hydroquinones, or the reductive conversion
of chlorocarbons to chloride anions plus carbon centered free radicals.
molybdenum (Mo):
a metalloid which is part of the active center of certain
oxidoreductases. These dehydrogenate xanthines, aldehydes, and sulfites.
The sequence is believed to occur first by reduction of Mo, then FAD,
and then O2. Superoxide radical (-OO*) is produced. Deficiency of Mo
has been associated with sulfite intolerance.
monoamine oxidase (MAO):
an oxidoreductase which dehydrogenates monoamines
converting them to terminal imines which spontaneously hydrolyze to
release ammonia and an aldehyde. MAO is found between the inner and
outer layers of mitochondria. It physiologically degrades certain
neurotransmitters and detoxifies numerous other amines.
monoatomic oxygen (O or *O* or [O]):
one atom of oxygen. This product of the
high energy split of diatomic oxygen (O2) adds to other O2 producing
ozone (O3). Ozone (O3) and chlorine dioxide (ClO2) can release one atom
of oxygen to certain organic compounds. O is produced and held by
cytochrome P 450 within the MFO system and added to xenobiotics. The
reaction produces epoxides and phenols.
monovalent:
an atomic or molecular species which has exchanged only
one electron; the characteristic of having lost one electron;
for a metal, possessing the charge of plus one.
multivalent:
able to exist in more than one oxidation state. The concept is
normally applied to transition metals but can also apply to redox active
organic molecules.
myeloperoxidase:
an oxido-reductase which reduces hydrogen peroxide to
produce water and which removes electrons from the chloride anion and
thereby generates hypochlorite anion (ClO-). This enzyme increases the
variety of strong caustic oxidants produced by immune cells to attack
invading pathogens.