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PubMed1989

The antioxidant and nutritional effects of tocopherols, ascorbic acid and beta-carotene in relation to processing of edible oils.

Tocopherols belong to a class of phenolic antioxidants which can inhibit lipid autoxidation by scavenging free radicals and by reacting with singlet oxygen. In vegetable oils alpha-tocopherol inhibits the effects of singlet oxygen during sensitized photoxidation. Ascorbic acid has a complex multi-function, acting as a hydrogen donor, as a metal inactivator, and as a peroxide destroyer. beta-Carotene protects lipids by interfering with photosensitized oxidation, and behaves as a reducing agent by trapping radicals. After processing of vegetable oils, about 60-70% of the tocopherols remain in the oil. However, the tocopherol content in processed vegetable oils, is generally above the optimum range for antioxidant activity. On the other hand, beta-carotene is almost completely removed during processing of vegetable oils. For antioxidant purposes, both beta-carotene and ascorbic acid must be added to vegetable oils after deodorization. The vitamin E activity of alpha-tocopherol may be attributed to its very efficient inhibition of in vivo lipid oxidation. In addition to its singlet oxygen quenching properties, beta-carotene has good radical-trapping properties at low partial pressures of oxygen, which prevail in healthy tissues. In biological systems, alpha-tocopherol and beta-carotene exhibit synergism by reinforcing their mutual activities. Synergism also takes place in a cascade where ascorbic acid can be regenerated at the expense of more oxidizable substrates. Our results suggest that singlet oxygen and free radical species may significantly contribute to the fluorescence formed from the interaction of DNA with linolenate hydroperoxides in the presence of iron and ascorbic acid. A better understanding of the biological effects of lipid oxidation products is needed to conserve the nutritional value of foods containing unsaturated lipids.

Antioxidants↗
PubMed1987

Positional reorganization in compound janus cells of Tetrahymena thermophila.

The janus mutations of Tetrahymena thermophila convert the large-scale organization of the dorsal surface of the cell into a mirror-image of the ventral surface, which is characterized by a second, abnormal, oral apparatus and by contractile vacuole pores to the left of the second oral area rather than the usual right. This conversion could be due either to a local change in the response to an unaltered positional system or to a more global reorganization of the system itself. janus homopolar doublets were used to distinguish between these two alternatives. Homopolar doublets can be made by fusing two similarly oriented cells in side-by-side parabiosis. Non-janus homopolar doublets typically possess two sets of normal oral structures with contractile vacuole pores to the right of each of them. In janus doublets, there are up to four sets of oral structures, with the abnormal oral structures located between the two sets of normal oral structures; contractile vacuole pores are situated to the right of the normal oral areas and to the left of the abnormal oral structures. Non-janus homopolar doublets are known to propagate their compound condition for a number of cell divisions, but also to regulate toward the singlet state through a progressive reduction in number of ciliary rows followed by loss of one of the two sets of major cell surface structures. janus homopolar doublets go through a corresponding regulation. As a consequence, the location of the abnormal oral structures relative to the normal ones is more variable in janus doublets than in janus singlets. Sometimes the abnormal oral structures shift to a position close to their normal counterparts and then the intervening CVP sets disappear. There is evidence for occasional fusion of an abnormal oral area with an adjacent normal oral apparatus, a condition that may be transitional to the singlet state. These observations are inconsistent with the idea of a fixed positional system and strongly suggest a global reorganization of the surface pattern in a manner consistent with predictions of an intercalation model that was first proposed to explain the regulation of non-janus doublets to singlets.

Animals↗
PubMed1999

Photoinactivation of vesicular stomatitis virus with fullerene conjugated with methoxy polyethylene glycol amine.

Fullerene is known to effectively produce mainly singlet oxygen by absorbing light energy, and therefore may be useful as a virucidal photosensitizer. This study was designed to investigate the virucidal activity of a water-soluble fullerene derivative, which is conjugated with methoxy polyethylene glycol amine to enhance its water solubility. Vesicular stomatitis virus (VSV) was inactivated upon illumination with this water-soluble fullerene, in a concentration- or dose-dependent manner. The titer of VSV was reduced by >5log 10 in the presence of 10 mg/ml (400 microM) fullerene derivative with 120 J/cm2 white light irradiation. VSV inactivation was inhibited by oxygen removal or by the addition of sodium azide, a known singlet oxygen scavenger. The substitution of H2O by D2O, which is known to prolong the lifetime of singlet oxygen, promoted the virucidal activity. These results indicate that singlet oxygen may play a major role in VSV photoinactivation by the water-soluble fullerene derivative. The concentration needed for virus inactivation is higher than that of other sensitizers such as methylene blue.

Antiviral Agents↗
PubMed2001

Activation of torularhodin production by Rhodotorula glutinis using weak white light irradiation.

The effects of the irradiation of weak white light on the growth of the red yeast Rhodotorula glutinis and its production of carotenoids were investigated. The ability of beta-carotene and torularhodin, which are final products of carotenoid biosynthesis in R. glutinis, to quench singlet oxygen has also been investigated. Weak white light irradiation that has no effect on the growth of Saccharomyces cerevisiae inhibited the growth of R. glutinis. Simultaneously, the production of torularhodin by R. glutinis markedly increased. In a mutant of R. glutinis, which exhibited increased production of torularhodin, an increase in torularhodin production was shown as a result of light irradiation during the logarithmic growth phase. An experiment using 3-(1,4-epidioxyl-4-methyl-1,4-dehydro-1-naphtyl) propionic acid clarified that torularhodin inhibited 2,5-diphenyl-3,4-benzofran decomposition by singlet oxygen quenching more strongly than did beta-carotene. This result is consistent with the report that carotenoids having a longer polyene chain may exhibit a more potent ability to quench singlet oxygen. These results suggest that the biosynthesis of carotenoids in R. glutinis may play an important role in protecting against oxidative damage caused by light irradiation, and in particular, torularhodin which has a potent singlet oxygen quenching ability may be important. We suggest that acquisition of the ability to produce torularhodin may be an important property for this yeast to promote its wider distribution in the natural world.

Journal Article↗
PubMedDate not supplied

Comparing beta-carotene, vitamin E and nitric oxide as membrane antioxidants.

Singlet oxygen initiates lipid peroxidation via a nonfree radical mechanism by reacting directly with unsaturated lipids to form lipid hydroperoxides (LOOHs). These LOOHs can initiate free radical chain reactions leading to membrane leakage and cell death. Here we compare the ability and mechanism by which three small-molecule membrane antioxidants (beta-carotene, alpha-tocopherol and nitric oxide) inhibit lipid peroxidation in membranes. We demonstrate that beta-carotene provides protection against singlet oxygen-mediated lipid peroxidation, but does not slow free radical-mediated lipid peroxidation. Alpha-Tocopherol does not protect cells from singlet oxygen, but does inhibit free radical formation in cell membranes. Nitric oxide provides no direct protection against singlet oxygen exposure, but is an exceptional chain-breaking antioxidant as evident from its ability to blunt oxygen consumption during free radical-mediated lipid peroxidation. These three small-molecule antioxidants appear to have complementary mechanisms for the protection of cell membranes from detrimental oxidations.

Animals↗
PubMed2004

Porphyrin depth in lipid bilayers as determined by iodide and parallax fluorescence quenching methods and its effect on photosensitizing efficiency.

Photosensitization by porphyrins and other tetrapyrrole chromophores is used in biology and medicine to kill cells. This light-triggered generation of singlet oxygen is used to eradicate cancer cells in a process dubbed "photodynamic therapy," or PDT. Most photosensitizers are of amphiphilic character and they partition into cellular lipid membranes. The photodamage that they inflict to the host cell is mainly localized in membrane proteins. This photosensitized damage must occur in competition with the rapid diffusion of singlet oxygen through the lipid phase and its escape into the aqueous phase. In this article we show that the extent of damage can be modulated by employing modified hemato- and protoporphyrins, which have alkyl spacers of varying lengths between the tetrapyrrole ring and the carboxylate groups that are anchored at the lipid/water interface. The chromophore part of the molecule, and the point of generation of singlet oxygen, is thus located at a deeper position in the bilayer. The photosensitization efficiency was measured with 9,10-dimethylanthracene, a fluorescent chemical target for singlet oxygen. The vertical insertion of the sensitizers was assessed by two fluorescence-quenching techniques: by iodide ions that come from the aqueous phase; and by spin-probe-labeled phospholipids, that are incorporated into the bilayer, using the parallax method. These methods also show that temperature has a small effect on the depth when the membrane is in the liquid phase. However, when the bilayer undergoes a phase transition to the solid gel phase, the porphyrins are extruded toward the water interface as the temperature is lowered. These results, together with a previous publication in this journal, represent a unique and precedental case where the vertical location of a small molecule in a membrane has an effect on its membranal activity.

Fluorescence Recovery After Photobleaching↗
PubMed2000

A photophysical and photochemical study of 6-methoxy-2-naphthylacetic acid, the major metabolite of the phototoxic nonsteroidal antiinflammatory drug nabumetone.

Nabumetone is a phototoxic nonsteroidal antiinflammatory drug used for the treatment of osteoarthritis. However, nabumetone is considered a prodrug with its metabolite 6-methoxy-2-naphthylacetic acid the active form. Photophysical and photochemical studies on this metabolite have been undertaken. It undergoes photodecarboxylation in aerated aqueous and organic solvents. In addition to the accepted photodegradation pathway for related molecules, a new mechanism that implies generation of the naphthalene radical cation from the excited singlet and addition of O2 prior to the decarboxylation process has been demonstrated. Evidence for the involvement of the excited singlet state in this mechanism have been obtained by steady-state and time-resolved fluorescence experiments. The fluorescence quenching by O2 and the shorter singlet lifetime in aerated solvents support this assignment. Laser flash photolysis also supports this mechanism by showing the noninvolvement of the triplet in the formation of the naphthalene radical cation. Finally, the well-known electron acceptor CCl4 acts as an efficient singlet quencher, enhancing the route leading to the radical cation, preventing intersystem crossing to the triplet and thus resulting in a dramatic increase in the yield of 6-methoxy-2-naphthaldehyde, the major oxidative decarboxylation product; this constitutes unambiguous proof in favor of the new mechanistic proposals.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Primary photophysical properties of ofloxacin.

Steady-state fluorescence has been used to study the excited singlet state of ofloxacin (OFLX) in aqueous solutions. Fluorescence emission was found to be pH dependent, with a maximum quantum yield of 0.17 at pH 7. Two pKa*s of around 2 and 8.5 were obtained for the excited singlet state. Laser flash photolysis and pulse radiolysis have been used to study the excited states and free radicals of OFLX in aqueous solutions. OFLX undergoes monophotonic photoionization from the excited singlet state with a quantum yield of 0.2. The cation radical so produced absorbs maximally at 770 nm with an extinction coefficient of 5000 +/- 500 dm3 mol-1 cm-1. This is confirmed by one-electron oxidation in the pulse radiolysis experiments. The hydrated electron produced in the photoionization process reacts with ground state OFLX with a rate constant of 2.0 +/- 0.2 x 10(10) dm3 mol-1 s-1, and the anion thus produced has two absorption bands at 410 nm (extinction coefficient = 3000 +/- 300 dm3 mol-1 cm-1) and at 530 nm. Triplet-triplet absorption has a maximum at 610 nm with an extinction coefficient of 11,000 +/- 1500 dm3 mol-1 cm-1. The quantum yield of triplet formation has been determined to be 0.33 +/- 0.05. In the presence of oxygen, the triplet reacts to form both excited singlet oxygen and superoxide anion with quantum yields of 0.13 and < or = 0.2, respectively. Moreover, superoxide anion is also formed by the reaction of oxygen with the hydrated electron from photoionization. Hence the photosensitivity due to OFLX could be initiated by the oxygen radicals and/or by OFLX radicals acting as haptens.

Anti-Infective Agents↗
PubMed2003

Metallophthalocyanines photosensitize the breakdown of (hydro)peroxides in solution to yield hydroxyl or alkoxyl and peroxyl free radicals via different interaction pathways.

Interactions of organic peroxides (R'OOR) and hydroperoxides (R'OOH), including H2O2, with excited triplet and singlet state metallophthalocyanines (MPc, M = Zn, Al) have been studied by T-T absorption decay and fluorescence quenching. The ensuing photochemical processes result in decomposition of (hydro)peroxides as assessed by photo-EPR (electron paramagnetic resonance) and spin trapping. In argon-saturated apolar solutions and low MPc concentrations, alkoxyl free radicals (*OR) were identified as the primary products of (hydro)peroxide breakdown. Similarly, photosensitized decomposition of symmetric disulfides results in the formation of sulfur-centered radicals. In air-free aqueous solutions, ROOH photosensitization always gave rise to a mixture of hydroxyl and peroxyl radical (*OOR) adducts in varying molar ratios. At high MPc concentrations, both in polar and in apolar solutions, the most abundant products of ROOH decomposition were identified as *OOR. This indicates a change in the predominant interaction pathway, most likely mediated by MPc exciplexes and involving H-atom abstraction from ROOH by MPc-cation radicals. The prevalence of MPc singlet vs. triplet state interactions was confirmed by the much higher singlet quenching rate constants (log kq up to 9.5; vs. log kT < or = 4.5). In contrast to the triplet quenching, singlet quenching rates were found to depend on the (hydro)peroxide structure, following closely the trend of varying *OR yields for different substrates. Thermodynamic calculations were performed to correlate experimental results with models for electronic energy and charge transfer processes in agreement with the Marcus theory (Rhem and Weller approximation) and Savéant's model for a concerted dissociative electron transfer mechanism.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

Lens alpha-crystallin and hypericin: a photophysical mechanism explains observed lens.

Determining whether alpha-crystallin (the major lens protein) affects the photophysics of hypericin, a photosensitizing agent found in various plants, such as St. John's Wort, is important. Hypericin shows promise in cancer and human immunodeficiency virus therapy but may harm individuals taking St. John's Wort extracts (for mild to moderate depression). Hypericin causes hypericism, which is characterized by cellular damage in light-exposed areas. Ocular tissues are at risk for photosensitized damage; thus, we investigated the effects on hypericin photophysics by alpha-crystallin. We measured the transient absorption spectra and the 1270 nm luminescence of singlet (1Deltag) oxygen produced from hypericin in the presence of alpha-crystallin. alpha-Crystallin complexes hypericin, extending the lifetime of its triplet excited state; the Stern-Volmer slope is negative, but not linear, after a saturation curve. Damage to the lens protein by hypericin is known to occur via singlet oxygen, which oxidizes methionine, tryptophan and histidine residues. Binding to alpha-crystallin does not inhibit singlet oxygen formation by hypericin. alpha-Crystallin reacts with singlet oxygen with a rate constant of 1.3 x 10(8) M(-1) s(-1). Thus, we anticipate that hypericin will be an effective photosensitizer in the lens.

Anthracenes↗
PubMed1980

Initiation of oxidative changes in foods.

Initiation of lipid peroxidation in foods may be accomplished by a variety of mechanisms. Two principal initiation reactions involve homolytic scission of preformed peroxides as catalyzed by metal ions and heme proteins and the reaction of activated oxygen species with the lipid substrate to yield peroxides and free radicals. Copper and cytochromes in the milk fat globule membrane may serve as focal points for initiation of lipid peroxidation by catalyzing homolytic scission of peroxides. Activated oxygen species which may be important in initiating oxidative changes in foods include singlet oxygen, hydroxyl radical, ozone, superoxide anion (perhydroxyl radical at low pH), and hydrogen peroxide. Chemical and enzymic reactions in biological materials can generate singlet oxygen, hydroxyl radical, superoxide anion, and hydrogen peroxide. Ozone is primarily a product of photoreactions in polluted air. Reactions involving singlet oxygen, hydroxyl radical, and ozone with food constituents ultimately can yield peroxides which decompose to initiate oxidative chain reactions. Superoxide anion and hydrogen peroxide are relatively inert toward organic molecules but can decompose to produce the more reactive singlet oxygen and hydroxyl radical. Inhibition of reactions initiated by reactive oxygen species in foods should be very important in preserving the oxidative stability of foods. This paper presents a brief review of possible initiation reactions for lipid peroxidation and inhibition of reactions of activated oxygen species that are of importance in food systems.

Chemical Phenomena↗
PubMed1991

Electron spin resonance investigation of tyrosyl radicals of prostaglandin H synthase. Relation to enzyme catalysis.

We have examined, by low temperature ESR, the protein-derived radicals formed by reaction of purified ram seminal vesicle prostaglandin H synthase (PHS). Upon addition of arachidonic acid or 5-phenyl-4-pentenyl-1-hydroperoxide (PPHP) to PHS reconstituted with Fe(III)-protoporphyrin IX (Fe-PHS) at -12 degrees C, an ESR spectrum was observed at -196 degrees C containing a doublet that rapidly converted into a singlet. These protein-derived radicals were identified as tyrosyl radicals. The addition of a peroxidase substrate, phenol, completely abolished the appearance of the doublet and suppressed the formation of the singlet but did not inhibit eicosanoid formation. Incubation of arachidonic acid with PHS reconstituted with Mn(III)-protoporphyrin IX (Mn-PHS) produced only a broad singlet that exhibited different power saturation behavior than the tyrosyl radicals and decayed more rapidly. This broad singlet does not appear to be a tyrosyl radical. No ESR signals were observed on incubation of PPHP with Mn-PHS, which has cyclooxygenase but not peroxidase activity. Eicosanoid synthesis occurred very rapidly after addition of arachidonic acid and was complete within 1 min. In contrast, the protein-derived radicals appeared at a slower rate and after the addition of the substrate reached maximal levels between 1 and 2 min for Fe-PHS and 4-6 min for Mn-PHS. These results suggest that the observed protein-derived radicals are not catalytically competent intermediates in cyclooxygenase catalysis by either Fe-PHS or Mn-PHS. The peroxidase activity appears to play a major role in the formation of the tyrosyl radicals with Fe-PHS.

Alkenes↗
PubMed1994

Characterization of the tyrosyl radicals in ovine prostaglandin H synthase-1 by isotope replacement and site-directed mutagenesis.

Several free radical species, attributed to tyrosyl radicals, have been previously observed by electron paramagnetic resonance (EPR) spectroscopy during reaction of pure ovine prostaglandin H synthase-1 (PGHS-1) with hydroperoxide or fatty acid substrates. The identity and location of amino acid residue(s) involved in formation of these radicals has been investigated using wild type and mutant PGHS-1 expressed in transfected COS-1 cells. Upon reaction with hydroperoxide, detergent extracts from microsomes of cells expressing wild type ovine PGHS-1 rapidly produced EPR signals made up of a broad component, resembling either the wide doublet or the wide singlet seen in reactions of the purified ovine enzyme, mixed with a variable proportion of a narrow component. Isotope replacement with perdeuterated tyrosine and phenylalanine in wild type PGHS-1 caused no change in enzymatic activity or capability to form a peroxide-induced radical, but the radical was an isotropic singlet without any wide features. This loss of splitting in the deuterated enzyme establishes that the wide radical signal in PGHS-1 is indeed a tyrosyl radical, validating the earlier assignment based on spectral similarities with a tyrosyl radical in ribonucleotide reductase. A Y385F mutation abolished cyclooxygenase but not peroxidase activity, and the peroxide-induced EPR was narrowed to a singlet essentially identical with that obtained with indomethacin-treated ovine enzyme. Isotopic replacement with perdeuterated tyrosine and phenylalanine in the Y385F mutant led to further narrowing of the peroxide-induced EPR to an isotropic singlet, establishing that this radical also involved a tyrosine residue. A Y355F mutant exhibited some decrease in cyclooxygenase activity, but the peroxidase activity and the peroxide-induced radical characteristics were not significantly different from those of the wild type enzyme, indicating that Tyr355 is not involved in tyrosyl radical formation in PGHS-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1992

Weak chemiluminescence of bilirubin and its stimulation by aldehydes.

Bilirubin in an alkaline solution exhibits a weak chemiluminescence (CL) under aerobic conditions. This spontaneous CL was markedly enhanced by the addition of various aldehydes. The fluorescent emission spectrum of bilirubin, excited by weak intensity light at 350 nm, coincided with its CL emission spectrum (peak at 670 nm). CL emission from bilirubin was not quenched by active oxygen scavengers. This suggests that triplet oxygen reacts with bilirubin, and forms an oxygenated intermediate (hydroperoxide) as a primary emitter (oxidative scission of tetrapyrrole bonds in bilirubin is not involved in this CL). The Ehrlich reaction (test for monopyrroles) and hydrolsulphite reaction (test for dipyrroles) on the CL reaction mixture and unreacted bilirubin showed no differences. When the CL was initiated by singlet oxygen, rather than superoxide anion, monopyrrole, was detected in the reaction products by gel chromatography. The inhibitory effect of a scavenger of singlet oxygen on CL was eliminated in the presence of formaldehyde. Therefore, triplet carbonyl, formed by singlet oxygen through the dioxetane structure in bilirubin, is not an emitter. The reaction mechanism of bilirubin CL and the formation of a hydroperoxide intermediate is discussed in relation to the chemical structure of luciferin molecules from bioluminescent organisms.

Acetaldehyde↗
PubMed2006

Monomeric azaheterofullerene derivatives RC59N: influence of the R moiety on spectroscopic and photophysical properties.

We have synthesised nine monomeric azaheterofullerene (AZA) derivatives, RC(59)N, with a wide variety of different side chains R and investigated their spectroscopic and photophysical properties in toluene and o-dichlorobenzene (ODCB). Measurements include their ground-state absorption spectra, molar absorption coefficient (epsilon(G)), fluorescence spectra, fluorescence quantum yields (Phi(F)), singlet-state lifetimes (tau(F)), triplet-state absorption spectra, triplet molar absorption coefficients (epsilon(T)), singlet oxygen (Phi(Delta)), and triplet state (Phi(T)) quantum yields. The replacement of a carbon by a nitrogen atom in the C(60) sphere strongly affects most of the spectroscopic and photophysical properties. The chemical nature of the R moiety has definite effects on these properties in contrast with minor effects on the chemical nature of the addends in [6,6]-ring bridged monoadduct methano[60]fullerene derivatives. These effects concern properties of the ground state, singlet excited state, and triplet states of our nine RC(59)N derivatives and in particular the values of photophysical parameters epsilon(G), epsilon(T), Phi(Delta), and Phi(T), which are significantly lower than those of analogous monoadduct [6,6]-ring bridged methano[60]fullerene derivatives.

Chlorobenzenes↗
PubMed1993

Genotoxicity of volatile and secondary reactive oxygen species generated by photosensitization.

Reactive oxygen species were generated in the gas phase by photosensitization involving illumination of Rose Bengal. Depending on whether the chromophore is dry or solubilized, this system produces either energy-transfer reactions leading to generation of singlet oxygen specifically, or a combination of energy-transfer and electron-transfer reactions, providing both singlet oxygen and reduced forms of oxygen, such as superoxide anion and hydrogen peroxide. In neither case were the reactive species mutagenic in strain TA104 of Salmonella typhimurium, which had been previously shown to be reverted by oxygen species generated by the hypoxanthine-xanthine oxidase system in aqueous medium. However, mixed oxygen species induced an increased lethality in a variety of DNA repair-deficient Escherichia coli strains. This genotoxic effect, mainly reparable by the uvrA and recA mechanisms, was efficiently prevented by the thiol N-acetyl-L-cysteine. Singlet oxygen itself failed to exert direct genotoxic effects, although secondary reactants produced by its reaction with cell components enhanced lethality in some repair-deficient bacteria. Distance-dependence analyses provided measurements of the lifetimes of the oxygen species generated in the gas phase.

Absorption↗
PubMed1995

A homogeneous immunofluorescence assay based on dye-sensitized photobleaching.

A novel homogeneous immunoassay requiring only one incubation step, and applicable in principle to the determination of low- as well as high-molecular-weight substances, has been developed. The method is based on (a) photooxidation by singlet oxygen (1O2) of a fluorescent substrate (1,3-diphenylisobenzofuran, DPBF) embedded in unilamellar vesicles on the surface of which antibody to the analyte antigen is covalently attached (DPBF-immunoliposomes); (b) generation of singlet oxygen, upon illumination, by a chromophore (erythrosine) covalently attached to an antibody (Ab*) or antigen (Ag*); (c) formation of a "sandwich"- or "competition"-type complex whereupon the singlet oxygen-generating chromophore conjugate (Ab* or Ag*) and immunoliposome-embedded DPBF are brought into close proximity. Competition- and sandwich-type model assay systems for the detection of protein antigens and viruses were investigated. The detection range with protein antigens in competition- and sandwich-type assays was three (10(-10) - 10(-7) M) and two (10(-10) - 10(-8) M) orders of magnitude, respectively. With poliovirus using a sandwich-type assay, the detection range was 10(2) - 10(6) plaque-forming units per milliliter (pfu/ml).

Animals↗
PubMed2001

Formation of nitrotyrosine by methylene blue photosensitized oxidation of tyrosine in the presence of nitrite.

Methylene blue photosensitized oxidation of tyrosine in the presence of nitrite produces 3-nitrotyrosine, with maximum yield at pH 6. The formation of 3-nitrotyrosine requires oxygen and increases using deuterium oxide as solvent, suggesting the involvement of singlet oxygen in the reaction. The detection of dityrosine as an additional reaction product suggests that the first step in the interaction of tyrosine with singlet oxygen generates tyrosyl radicals which can dimerize to form dityrosine or react with a nitrite-derived species to produce 3-nitrotyrosine. Although the chemical identity of the nitrating species has not been established, the possible generation of nitrogen dioxide (*NO(2)) by indirect oxidation of nitrite by intermediately produced tyrosyl radical, via electron transfer, is proposed. One important implication of the results of this study is that the oxidation of tyrosine by singlet oxygen in the presence of nitrite may represent an alternative or additional pathway of 3-nitrotyrosine formation of potential importance in oxidative injures such as during inflammatory processes.

Animals↗