N-acetyl-L-cysteine (NAC or NALC):
the N-acetylated derivative of the
naturally occuring amino acid L-cysteine. NAC is more stable and has a
longer shelf life than cysteine (cys). Both NAC and cys are important
precursors to numerous oxidoreductases and transcription factors which
possess thiol groups. Supplemental cys from either source supports
glutathione synthesis. NAC and cys are useful in research as reductants.
NADH:
the reduced form of nicotinamide-adenine-dinucleotide; NAD+ which
has accepted two electrons and one proton; a reductant source for
numerous reductases. NADH is produced by glycolysis, the tricarboxylic
acid cycle, and other dehydrogenases. The electrons of NADH can be
used to produce ATP by oxidative phosphorylation in the mitochondria.
NADPH:
similar to NADH with an extra phosphate group. NADPH activates
a different set of reductases and is produced by action of the hexose
monophosphate shunt. The reducing power of NADPH is mostly used for
synthesis and for maintenance of intracellular thiols in the reduced state.
naphthoquinone (NQ):
a quinone possessing one aromatic ring coincident to
one of its ethylene bridges. Many naturally occuring naphthoquinones
have been found in medicinal herbs known to be immunostimulatory,
antiinfective, antineoplastic, and antiparasitic.
Nernst equation:
a formula developed by Nernst to predict the voltage and direction
of a half reaction. The formula is conventionally expressed as:
E = E'o + 2.303 RT/nF x log[oxidant]/[reductant]. It relates the
electromotive force (voltage) of any half reaction to the ambient
temperature, type(s) of reactant(s) present, and the concentration(s)
of the reactant(s). It can be used to predict whether or not a
particular redox reaction will take place and to what extent.
It can also be used to predict the voltage produced by a battery,
or the voltage necessary to drive an electrolysis or an
electroplating function.
nicotinamide-adenine-dinucleotide (NAD+):
a cofactor and carrier of reducing
equivalents which takes up a hydride (H-) equivalent upon action of
various dehydrogenases. NAD+ is composed of nicotinamide covalently
linked to a sugar molecule which is covalently linked to adenine.
A quaternary nitrogen at the nicotinamide group enables the molecule to
possess a positive charge. Like a pyridinium, the quaternary nicotinamide
group can accept one electron to become a semireduced radical. Upon
acceptance of one hydrogen atom it then becomes the fully reduced NADH.
nicotinamide-adenine-dinucleotide phosphate (NADP+):
similar to NAD+ but possessing an additional phosphate group.
nitric oxide (*NO):
a compound composed of only one atom each of
nitrogen and oxygen. *NO is a free radical which can add to the pi
bonds of certain molecules or couple with another free radical. Upon
coupling with hydroperoxyl radical (HOO*) peroxy nitric acid is produced
(HOONO) which readily decomposes to hydroxyl radical (HO*) and nitrogen
dioxide (*NO2). This strategy enables killer cells to destroy pathogens
and tumors. *NO is synthesized by nitric oxide synthase from the amino
acid arginine. *NO also serves physiologic cell to cell signal functions
such as the control of vasodilitation.
nitric oxide synthase (NOS):
the enzyme which in a multistep process generates nitric oxide (*NO)
from NADPH, oxygen, and arginine. Its activity is induced by certain
physiologic triggers which call for vasodilation, *NO being an agent
of this signal. NOS activity also accumpanies the action of killer cells
which produce *NO as a precursor to peroxynitric acid.
nitrosoureas:
a class of chemotherapeutic agents which reversibly inhibit
glutathione reductase. This cytostatic effect demonstrates the dependency
of proliferating cells on reducing agents, and thiols in particular.
Nitrosoureas are also useful in research to study various effects of an
increase in the GSSG/GSH ratio.
N-ethylmaleimide (NEM):
an alkylating agent which irreversibly binds to thiols.
NEM is useful as a research tool to inhibit and to identify enzymes
which require thiols to be active.
nordihydroguaiaretic acid (NDGA):
a polyphenol extractable from chapparal/creosote bush useful
as an antiseptic agent. Chapparal has traditionally
been used as an herbal remedy against infection and cancer.
nuclear factor kappa B (NF-kappa-B):
a transcription factor found within the cytoplasm of certain cell types.
It is bound to inhibitory factor kappa B (I-kappa-B) from which it
can be released upon activation by various physiologic triggers.
Once released, NF-kappa-B migrates into the nucleus where it associates
with activator protein 1 (AP-1) thus forming a transcription complex.
As a result, messenger RNA is produced, which migrates back out of the
nucleus and associates with a ribosome. There immunoactive cytokines
are synthesized. Upon release to the outside of the cell, cytokines trigger
a strong generalized immune response. Exposure to oxidants causes
the conversion of glutathione (GSH) to glutathione disulfide (GSSG).
GSSG causes NF-kappa-B to be released from I-kappa-B. Thus indirectly,
oxidants trigger production of immunoactive cytokines.
nucleophile:
a reactive molecule or group which is attracted towards and
tends to react with the electropositive pole of another molecule.
Nucleophiles are themselves electron rich and alkaline.
Examples are primary amines and thiols.
