a genome or its corresponding protein which controls both reproduction and apoptosis of the cell in response to a variety of physiologic triggers. P53 contains redox active thiol groups making P53 function sensitive to the redox balance of the cell. Aberrant P53, as occurs when its corresponding genome is mutated, can result in excessive cellular proliferation or resistance to apoptosis, either or both of which are known to occur in cancer cells. Thus mutant P53 is an oncogene.
para-aminobenzoic acid (PABA):
an aromatic ring with a carboxyl group at carbon one and an amino group at carbon four; a precursor to folate synthesis in bacteria. Sulfonylamides are structural analogues of PABA and as such competitively block incorporation of PABA in the synthesis of folate. PABA, sulfonylamides, and aminobenzene compounds in general are quenchers of singlet oxygen.

the characteristic of being attracted towards a magnetic field but not able to hold a magnetic charge. Free radicals are all paramagnetic due to the unpaired electron they possess which is also a tiny magnet.

1,1'-dimethyl-4,4'-dipyridilium dichloride; a dimer of N-methyl pyridinium rings linked at the number four carbons and able to conjugate. A positively charged quaternary nitrogen atom is present at each of the two ends of the molecule bound to a methyl group. This structure can readily accept electrons from various physiologic donors one or two at a time. Its semireduced form is a relatively stable free radical due to the extensive conjugation. Like a semireduced flavin (*FADH) or quinone (*QH), semireduced paraquat readily passes electrons one at a time to oxygen producing of superoxide (-OO*) and hydroperoxide (HOO*) radicals. Paraquat is used as an herbicide in agriculture, and as a research tool in biochemistry to study the effects of the introduction of superoxide or the effectiveness of quenchers of superoxide. Delayed toxic effects accrue to the lungs, liver, kidneys, and possibly the CNS when ingested.

a compound composed of a ring of six carbon atoms, an oxo group at carbons number 1 and 4, and double bonds between carbons 2 and 3 and between carbons 5 and 6; two carbonyl groups connected by two ethylene bridges forming a six membered ring. Paraquinones are medium strength oxidants able to accept two hydrogen atoms to become hydroquinones or paradihydroxybenzenes. Paraquinones possess four conjugated pi bonds (more if side chains or rings are present) which facilitate stabilization of the semireduced state. Paraquinones readily redox cycle under biological conditions due to the presence of both reductants and oxidants of various potentials. These are able to transfer electrons to or from the paraquinones.

Pasteur effect:
the inhibition of fermentation by oxygenation.

pentose pathway:
another term for the hexose monophosphate shunt. The pentose pathway produces large quantities of NADPH which activate numerous reductases.

peroxide (ROOR'):
a family of compounds which possess two oxygen atoms covalently bound to each other by sigma bonds forming a bridge within the rest of the molecule. Organic peroxides can be reduced to alcohols by the addition of two hydrogen atoms, one to each oxygen of the bridge. One equivalent reductions produce an alcohol and an alkoxyl radical.

any of a family of enzymes which reduce peroxides whether hydrogen peroxide, lipid hydroperoxide, dialkylperoxide, or endoperoxide. Peroxidases must have a source of reductant to accomplish this. In the case of catalase, one molecule of hydrogen peroxide can serve as reductant producing oxygen, while another is reduced to water. Glutathione peroxidase accepts hydrogen atoms from glutathione (GSH) and uses these to reduce numerous peroxide types. Other peroxidases can abstract electrons from a wide variety of donors to accomplish peroxide reduction.

peroxynitric acid (HOONO):
an acid composed of a peroxide bridge between a hydrogen atom and a nitrogen atom with attached oxo group. HOONO is produced in vivo by activated killer cells by the coupling of two free radicals hydroperoxyl (HOO*) and nitric oxide (*NO). HOONO decomposes spontaneously to produce the nitrogen dioxide radical (*NO2) plus the highly cytotoxic hydroxyl radical (HO*).

phase I detoxification:
the first step in catabolic elimination of certain insoluble organic molecules such as steroid hormones, aromatic compounds, and xenobiotics; the action of the mixed function oxidase system in which cytochrome P 450 adds one atom of oxygen to the substrate converting it to an epoxide or an aromatic hydroxide (phenol).

phase II detoxification:
the second step of catabolic elimination of various compounds which were hydroxylated by the phase I system; conjugation of various xenobiotics or metabolites with another molecule which renders the product water soluble enabling elimination in the bile or urine. In this context conjugation means the covalent attachment of a water soluble group (not the coreactivity of pi bonds as in other contexts). These addition reactions can be esterifications or thiol additions. Precursors commonly used are glutathione, taurine, sulfate, glycine, and glucaronic acid.

a tricyclic compound naturally occurring in pseudomonas species of bacteria. The central ring contains 2 nitrogen atoms as imines which are conjugated and redox active. Thus each molecule of phenazine can reversibly take up and carry 2 atoms of hydrogen.

phenol (Ar-OH):
an aromatic compound having a hydroxyl group attached to one of the carbon atoms of the aromatic ring.

phenoxyl radical (Ar-O*):
the semioxidized form of phenol which has one atom of hydrogen removed from the hydroxyl oxygen. Phenoxyl radical is stabilized by resonance of the unpaired electron among four sites among its three conjugated pi bonds. Phenoxyl radical can be readily reduced to phenol by numerous stronger reductants. Phenoxyl radicals can couple to produce dimers known as diphenoquinones.

phorbol (TPA):
12-O-tetradecanoylphorbol-13-acetate; a growth promotor which can be applied externally to cells in vivo or in vitro to stimulate mitosis and transformation to neoplasia. TPA initiates a complex series of intracellular responses some of which involve redox sensitive compounds.

6-phosphogluconate dehydrogenase:
an oxidoreductase which catalyses the transfer of reducing equivalents from 6-phosphogluconate to NADP+; a key producer of NADPH as part of the hexose monophosphate shunt.

the addition of a phosphoryl group (PO3--). This process facilitates energy metabolism, metabolite preparation, biosynthesis, and physiologic signal transduction.

the phenomenon of the absorbtion of the energy from photons by certain molecules which hold or process this energy releasing it later usually at a frequency or wavelenth different from that originally absorbed.

the stimulation of the uptake of hydrogen atoms by light. Compounds containing pi bonds (especially conjugated pi bonds) can absorb photon energy and be chemically photoactivated. This converts them to a triplet state also known as a diradical. As a diradical the energized molecule becomes a much stronger oxidant causing it to abstract hydrogen more readily from other potential donors. Photoactivation thus causes a redox reaction to take place which ordinarily would never occur.

pi bond:
a type of covalent bond usually formed from two p orbitals which are oriented in the same plane perpendicular to the long axis of a sigma bond. The orbitals form two clouds which are sausage or bean shaped, one on each side of the sigma bond which is spindle shaped. The pi bond is of a slightly higher potential energy level than a sigma bond and is therefore more easily broken and chemically more reactive. Pi bonds can trap free radicals, polymerize, accept hydrogen atoms, conjugate, and absorb photons to become diradicals.

picogram (pcg):
one trillionth of a gram; one millionth of a millionth of a gram; 10 exp -12 gram.

plastoquinone (PQ-9):
2,3-dimethyl-6-nonaprenyl-1,4-benzoquinone. An important carrier of reducing equivalents in chloroplasts as part of the photosynthetic process. Plastoquinone is present in all green plants, in the fresh juices of green plants, and with crude extracts of green plants.

5-hydroxy-2-methyl-1,4-naphthoquinone; droserone; a NQ naturally occuring in lead wort (numerous species of Plumbaginaceae), in venus fly trap (Dionaea muscipula), several species of Droseraceae, Diospyros, Drosophyllum, Ceratostigma, etc. Numerous herbal remedies utilize these species. Carnivora is a standardized extract of Dionaea muscipula in ethyl alcohol made in Germany. In India the root of plumbago is the medicament commonly known as Chita or Chitraka. Plumbagin has shown immunostimulatory, antiviral, antibacterial, and antineoplastic effects.

a class of ubiquitous amines which are synthesized prior to and during mitosis. Polyamines are necessary for cell growth, division, protein synthesis, and the integrity of certain organelles. Common naturally occuring polyamines are spermine, spermidine, cadaverine and putrescine.

polyamine oxidase (PAO):
any of a class of enzymes which degrades polyamines converting them to aldehydes by the process of oxidative deamination. PAO's can attack primary and secondary amino groups.

an aromatic compound with two or more hydroxyl groups substituting for hydrogen in the benzene ring. Naturally occuring diphenols have two hydroxyl groups in either the ortho (1,2), meta (1,3) or para (1,4) positions. In triphenols the hydroxyl groups are usually adjacent (1,2,3). Common examples are the many esters of gallic acid. Many naturally occuring polyphenols also have a flavone, anthocyanidin, or other bioflavonoid structure. Many are polymers of bioflavonoids. Polyphenols are more active than monophenols as reductive antioxidants. Ortho-diphenols (also known as catechols or orthohydroquinones) and para-diphenols (also known as parahydroquinones) readily autooxidize to become ortho- and para-quinones respectively. Oxidized polyphenols are bitter tasting, astringent, and often irritating, have documented antibacterial and antineoplastic effects, and react with primary amines to form imines which can polymerize. The products of oxidized polyphenols and amines are often brown or tan in color, hense the name tannins as applied to mixtures of polyphenols or oxidized polyphenols.

polyunsaturated fatty acid (PUFA):
a long chain hydrocarbon with a terminal carboxyl group and two or more carbon-carbon double bonds along its length. The double bonds exist only in the cis configuration. They are seperated by two or more single bonds, thus they are not conjugated. Any hydrogen atom alpha to a double bond, especially the one in between two double bonds, is more readily extractable by strong oxidants as compared to fully saturated hydrocarbons. This vulnerability allows for PUFA's to be further modified to become conjugated dienes or lipid peroxides.

able to exist in more than one oxidation state.

porphin and porphyrin:
a class of compounds composed of four heterocyclic rings each ring containing five members (four of carbon and one of nitrogen) with the nitrogen held centrally. The structure possesses eleven conjugated pi bonds with interesting spectral, photochemical, free radical stabilizing, and redox active characteristics. The center provides four nitrogenous ligands which bind cationic metals such as magnesium, iron, or copper. Metalloporphins are utilized in electron transfer, oxygen transfer, and photosynthesis.

primary amine (R-CH2-NH2):
a nitrogen atom covalently bound to two atoms of hydrogen and one of carbon. Examples are: amino acids, polyamines, neurotransmitters, ptomaines, guanine, cytosine, etc.

a substance selected for its specific form and chemical action, which is introduced in vivo or in vitro (in the presence of biological molecules such as enzymes and substrates). They are used, to study the function of a particular enzyme, metabolic pathway, receptor, or trigger. Probes enable us to discover the molecular mechanisms underlying numerous biochemical functions. Probes are usually analogues of naturally occurring metabolites, or they may be radio-isotopes, drugs, or dyes.

any substance or condition favorable to a process of oxidation. Examples are: the introduction of oxidants, the charging of an anodic plate, the removal of or inactivation of normally available reductants, the cutting off of any influx of new reductants, the introduction of catalysts which facilitate the transfer of electrons from the substances being oxidized to the available oxidants.

a chemical reaction which perpetuates itself by the reaction of free radicals which produce new free radicals which go on to react again.

any substance or condition favorable to the process of reduction. Examples are: the introduction of reductants, the charging of a cathodic plate, the removal or inactivation of normally available oxidants, the cutting off of any influx of new oxidants, the introduction of catalysts which facilitate the transfer of electrons from the available reductants to the substances being reduced, the removal or inactivation of catalysts which otherwise facilitate oxidation. The detoxification of certain metallic cations by chelation, and the phase II conjugation of quinones, are examples of the elimination of pro-oxidant catalysts.

prostaglandin (PG):
a class of docosoids which function as mediators of physiologic cell signal mechanisms. These control functions as diverse as inflammation and blood coagulation. Some of the prostaglandin conversion pathways involve redox reactions or oxygenations.

prosthetic group:
a molecular species attached to a polypeptide to produce an active enzyme. Examples are: the binding of FAD to an apoprotein to produce a dehydrogenase, or the insertion of a metalloporphin into yet another apoprotein to produce a cytochrome.

protein disulfide isomerase (PDI):
an oxidoreductase containing two redox active cysteine residues localized to the endoplasmic reticulum where it serves to regulate the correct folding of proteins as they emerge from ribosomes. PDI can be activated by thioredoxin reductase. PDI serves as part of the conversion process of proline to hydroxy proline in collagen synthesis. PDI is a cofactor in the release of triacylglycerols from the liver. PDI is able to convert dehydroascorbate to ascorbic acid.

protein kinases:
a family of enzymes which catalyze the phosphorylation of specific amino acid residues of their target proteins as part of numerous intracellular signal mechanisms. Common targets of this action are: tyrosine, serine, histidine, and threonine.

products of protein putrifaction including amines produced by the decarboxylation of amino acids.

putrescine (NH2-CH2-CH2-CH2-CH2-NH2):
a polyamine and precursor to other polyamines; the decarboxylation product of ornithine; an amine produced by putrifying bacteria.

heterocyclic compounds composed of 5 carbon atoms and 1 nitrogen atom. Niacin (vitamin B3) and the dinucleotides of nicotinamide (NADH and NADPH) are derivatives of pyridines.

a quaternary ammonium analogue of pyridine; a heterocyclic aromatic ring similar to benzene but replacing one of the ring members with a nitrogen atom covalently bound to an alkyl group. Thus a quaternary ammonium atom of positive charge substitutes for the normally neutral and quadrivalent carbon atom. Pyridinium rings are readily able to accept one electron, due to their positive charge and their extensively conjugated pi bonds, to form a neutral semireduced radical. This function explains the first electron transfer to the physiologic electron carrier NAD+ which contains a pyridinium ring (nicotinamide) at its redox active site. The semireduced radical subsequently accepts a whole hydrogen atom to become NADH. The herbicide paraquat (which is a dimer of two pyridinium rings) redox cycles by this same mechanism. It passes electrons one at a time to diatomic oxygen so producing extensive quantities of superoxide (-OO*). The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is dehydrogenated by monoamine oxidase (MAO) to 1-methyl-4-phenylpyridinium (MPP+). Like paraquat, MPP+ is believed to redox cycle and produce an overabundance of superoxide. The substantia nigra, being especially vulnerable to superoxide/hydroperoxyl toxicity, degenerates resulting in Parkinson's disease (paralysis agitans). The CNS toxicity of MPTP in experimental animals is inhibited by the MAO inhibitor selegiline/ deprenyl/Eldepryl.

azole; imidole; a 5 atom heterocyclic compound composed of 4 carbons and 1 nitrogen, the carbons bare double bonds but not the nitrogen. A group present in numerous biologic molecules including porphyrins, heme, porphobilinogen, and bilirubins.

pyrroloquinoline quinone (PQQ):
a tricyclic compound composed of 11 carbon atoms and 2 nitrogen atoms among its three rings, three carboxyl groups bound externally, and an orthoquinone group at the middle ring. The rings are unsaturated resulting in extensively conjugated pi bonds. The orthoquinone form is readily reducible to an enediol. PQQ can redox cycle in vivo. It is synthesized by certain bacteria in which it has been shown to be part of the redox active center of certain glucose and alcohol dehydrogenases. Until recently PQQ was erroneously thought to be part of the redox active center of the mammalian diamine oxidases. PQQ is a naturally occuring compound in the diet. PQQ has been shown to convey significant physiologic benefits such as improved resistance to lead toxicity, ischemia-reperfusion injury, cataract formation, corticosteroid injury, hepatotoxins, and infection. PQQ supports the function of lysyl oxidase, though is probably not part of its structure.

pyruvic acid (CH3-CO-COOH):
alpha-keto-n-propanoic acid; the final product of glycolysis under aerobic conditions; the precursor to lactic acid under anaerobic conditions when used instead of oxygen as an electron acceptor. Pyruvic acid can be shuttled unto the mitochondria where it is further processed as a fuel molecule.