Mechanism for the generation of superoxide anion and singlet oxygen during heme compound-catalyzed linoleic acid hydroperoxide decomposition

A meta-analysis and review examining a possible role for oxidative stress and singlet oxygen in diverse diseases

From kinetic data (k, T) we calculated the thermodynamic parameters for various processes (nucleation, elongation, fibrillization, etc.) of proteinaceous diseases that are related to the β-amyloid protein (Alzheimer's), to tau protein (Alzheimer's, Pick's), to α-synuclein (Parkinson's), prion, amylin (type II diabetes), and to α-crystallin (cataract). Our calculations led to ΔG^≠ values that vary in the range 92.8-127 kJ mol^-1 at 310 K. A value of ∼10-30 kJ mol^-1 is the activation energy for the diffusion of reactants, depending on the reaction and the medium. The energy needed for the excitation of O₂ from the ground to the first excited state (¹Δ_g, singlet oxygen) is equal to 92 kJ mol^-1 So, the ΔG^≠ is equal to the energy needed for the excitation of ground state oxygen to the singlet oxygen (¹Δ_g first excited) state. The similarity of the ΔG^≠ values is an indication that a common mechanism in the above disorders may be taking place. We attribute this common mechanism to the (same) role of the oxidative stress and specifically of singlet oxygen, (¹Δ_g), to the above-mentioned processes: excitation of ground state oxygen to the singlet oxygen, ¹Δ_g, state (92 kJ mol^-1), and reaction of the empty π* orbital with high electron density regions of biomolecules (∼10-30 kJ mol^-1 for their diffusion). The ΔG^≠ for cases of heat-induced cell killing (cancer) lie also in the above range at 310 K. The present paper is a review and meta-analysis of literature data referring to neurodegenerative and other disorders.

Accumulation of Paprika Carotenoids in Human Plasma and Erythrocytes

The accumulation (incorporation) of paprika carotenoid in human plasma and erythrocytes was investigated. A paprika carotenoid supplement (14 mg/day) was ingested for 4 weeks by 5 young healthy volunteers (3 men and 2 women). After 2 weeks of carotenoid ingestion, the carotenoid levels in plasma and erythrocytes increased by 1.2-fold and 2.2-fold, respectively. Characteristic carotenoids found in paprika (capsanthin, cucurbitaxanthin A, and cryptocapsin) were detected in both plasma and erythrocytes. An oxidative metabolite of capsanthin (capsanthone) was also found in both plasma and erythrocytes.

Effect of α-tocopherol on the hemin-catalyzed decomposition of 1-palmitoyl-2-linoleoyl-3-sn-phosphatidylcholine 13-hydroperoxide in micelles and liposomes

The secondary process of lipid peroxidation produces some toxic aldehydes. Since this process takes place via free radical reaction in lipophilic circumstances, α-tocopherol would suppress the formation of such aldehydes by trapping free-radical intermediates. This study reports the effect of α-tocopherol on the hemin-catalyzed decomposition of 1-palmitoyl-2-linoleoyl-3-sn-phosphatidylcholine 13-hydroperoxide (PLPC-OOH) in micelles and liposomes. PLPC-OOH and α-tocopherol were reacted with hemin in micelles, and the reaction products were characterized to be 1-palmitoyl-2-(α-tocopheroxy-12,13-epoxyoctadecenoyl)-3-sn-phosphatidylcholines (T-epoxyPLPC) and known compounds, 1-palmitoyl-2-[(8a-dioxy-α-tocopherone)-12,13-epoxyoctadecenoyl]-3-sn-phosphatidylcholines (TOO-epoxyPLPC) and α-tocopherol dimer. The hemin-catalyzed decomposition of PLPC-OOH in micelles produced hexanal as one of secondary aldehydic products. α-Tocopherol suppressed the formation of hexanal, and α-tocopherylquinone, α-tocopherol dimer, TOO-epoxyPLPC, and T-epoxyPLPC were detected during the reaction. In liposomes, α-tocopherol could partially suppress the formation of hexanal, and the main products were TOO-epoxyPLPC and α-tocopherol dimer. The results indicate that α-tocopherol may suppress the formation of hexanal by trapping the epoxyperoxyl and epoxyalkyl radicals derived from PLPC-OOH.

Singlet molecular oxygen generated by biological hydroperoxides

The chemistry behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chemical generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the production of excited carbonyl species and singlet molecular oxygen in the mechanism of generation of chemiluminescence in biological system. In particular, attention has been focused on the potential generation of singlet molecular oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet molecular oxygen from reactions involving the decomposition of biologically relevant hydroperoxides, especially from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chemical aspects related to the mechanism of singlet molecular oxygen generation from different biological hydroperoxides.

Luminescence of imidazo[1,2-a]pyrazin-3(7H)-one compounds

In this review I will discuss chemical principles of the luminescence of imidazo[1,2-a]pyrazin-3(7H)-one compounds described to date. The review is composed of two main parts, the first dealing with the bioluminescence of coelenterate luciferin "coelenterazine" and Cypridina luciferin in marine organisms and the second with the chemiluminescence of these luciferins and their analogues. In the second section, possible applications of chemiluminescence and enhanced chemiluminescence in the area of bioassay are also discussed.

4,5-Dimethylthio-4‘-[2-(9-anthryloxy)ethylthio]tetrathiafulvalene, a Highly Selective and Sensitive Chemiluminescence Probe for Singlet Oxygen

4,5-Dimethylthio-4'-[2-(9-anthryloxy)ethylthio]tetrathiafulvalene has been designed and synthesized as a highly selective and sensitive chemiluminescence (CL) probe for singlet oxygen ((1)O(2)). The design strategy for the probe is directed by the idea of photoinduced electron-transfer process and carried out through the incorporation of electron-rich tetrathiafulvalene unit into a reactive luminophore of anthracene specific for (1)O(2). Upon reaction with reactive oxygen species (ROS), such as hydrogen peroxide, hypochlorite, superoxide, hydroxyl radical, or (1)O(2), the probe exhibits both strong CL response to and high selectivity for (1)O(2) only, rather than the other ROS. This remarkable CL property permits (1)O(2) to be distinguished easily from the other ROS and makes the probe possible to be used widely for (1)O(2) detection in many chemical and biological systems and even in light water (H(2)O) environments. This applicability has been demonstrated by monitoring the (1)O(2) generation in a metal-catalyzed decomposition system of tert-butyl hydroperoxide. Moreover, the CL reaction mechanism of the present system is also discussed, clearly confirming that the introduction of electron-rich tetrathiafulvalene into the 9-position of anthracene can greatly activate its reactivity toward (1)O(2).

Involvement of MEK/ERK pathway in cephaloridine-induced injury in rat renal cortical slices

We have previously reported that free radical-mediated injury induced by cephaloridine (CER) is enhanced by phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, in rat renal cortical slices. We have also shown that PKC activation in mitochondria is involved in CER-induced nephrotoxicity in rats. We investigated the role of a downstream PKC pathway, a MEK/ERK pathway, in free radical-induced injury in rat renal cortical slices exposed to CER. Immediately after preparing slices from rat renal cortex, the slices were incubated in the medium containing MEK inhibitors. ERK1/2 activation was determined by Western blot analysis for phosphorylated ERK (pERK) 1/2 protein in nucleus fraction prepared from the slices exposed to CER. Prominently, CER caused not only increases in lipid peroxidation as an index of free radical generation and in LDH leakage as that of cell injury in the slices, but also marked activation of ERK1/2 in nucleus fraction. PD98059 and U0126, MEK1/2 inhibitors, significantly attenuated CER-induced increases in lipid peroxidation and LDH leakage in the slices. PD98059 also suppressed ERK1/2 activation in nucleus fraction prepared from the slices treated with CER. Inhibition of other MAP kinase pathways, p38 MAP kinase and c-Jun N-terminal kinase (JNK) had no effect on CER-induced increases in lipid peroxidation level and LDH leakage in the slices. The present results suggest that a MEK/ERK pathway down stream of a PKC pathway is probably involved in free radical-induced injury in rat renal cortical slices exposed to CER.

Singlet molecular oxygen generated from lipid hydroperoxides by the russell mechanism: studies using 18(O)-labeled linoleic acid hydroperoxide and monomol light emission measurements

The decomposition of lipid hydroperoxides into peroxyl radicals is a potential source of singlet oxygen ((1)O(2)) in biological systems. We report herein on evidence of the generation of (1)O(2) from lipid hydroperoxides involving a cyclic mechanism from a linear tetraoxide intermediate proposed by Russell. Using (18)O-labeled linoleic acid hydroperoxide (LA(18)O(18)OH) in the presence of Ce(4+) or Fe(2+), we observed the formation of (18)O-labeled (1)O(2) ((18)[(1)O(2)]) by chemical trapping of (1)O(2) with 9,10-diphenylanthracene (DPA) and detected the corresponding (18)O-labeled DPA endoperoxide (DPA(18)O(18)O) by high-performance liquid chromatography coupled to tandem mass spectrometry. Spectroscopic evidence for the generation of (1)O(2) was obtained by measuring (i) the dimol light emission in the red spectral region (lambda > 570 nm); (ii) the monomol light emission in the near-infrared (IR) region (lambda = 1270 nm); and (iii) the quenching effect of sodium azide. Moreover, the presence of (1)O(2) was unequivocally demonstrated by the direct spectral characterization of the near-IR light emission. For the sake of comparison, (1)O(2) deriving from the H(2)O(2)/OCl(-) and H(2)O(2)/MoO(4)(2)(-) systems or from the thermolysis of the endoperoxide of 1,4-dimethylnaphthalene was also monitored. These chemical trapping and photoemission properties clearly demonstrate that the decomposition of LA(18)O(18)OH generates (18)[(1)O(2)], consistent with the Russell mechanism and pointing to the involvement of (1)O(2) in lipid hydroperoxide mediated cytotoxicity.

Rapid determination of rice seed vigour by spontaneous chemiluminescence and singlet oxygen generation during early imbibition

Using a highly sensitive single photon counter, a spontaneous chemiluminescence (CL) study on rice (Oryza sativa L.) seeds stored in different years was carried out. We first observed that the degree of ageing in rice seeds was related to the intensity of spontaneous CL during early imbibition (0-30 min). Rice seeds stored for a shorter time had a stronger intensity of CL in early imbibition. The germination rate of rice seeds showed an obvious positive correlation with the intensity of spontaneous CL. Singlet oxygen ((1)O(2)) in rice seeds during early imbibition was investigated by a CL method using a cypridina luciferin analogue, 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo [1,2alpha] pyrazin-3-one (MCLA), as a selective CL probe. Additional experimental evidence for the formation of (1)O(2) came from the quenching effect of sodium azide (NaN(3)) on MCLA-mediated rice seeds' CL. Analysis based on the experimental results demonstrated that spontaneous CL in rice seeds during early imbibition was mainly contributed by singlet oxygen ((1)O(2)).

Localization of tumor by chemiluminescence probe during photosensitization action

As a chemiluminescence (CL) probe, 3,7-dihydro-6-[4-[2-(N'-(5-fluoresceinyl) thioureido)ethoxy]phenyl]-2-methylimidazo[1,2-a]pyrazin-3-one dosium salt (FCLA) can sensitively and specifically react with singlet oxygen ((1)O(2)) and superoxide (O(2)(-)). Based on the fact that photosensitization action involves (1)O(2) generation, this report presents a novel method for localization of tumor mediated by FCLA. In experiments, FCLA was used as an optical reporter of (1)O(2) produced from photosensitization reaction of hematoporphyrin derivative. The effects of azide inhibition and deuterium enhancement on photosensitized CL indicated that (1)O(2) molecules generated during photosensitization action could be measured and imaged. In vivo experiments in vivo with tumor-bearing nude mice showed a clear CL image of tumor. The study suggests that CL imaging method may be applicable to the detection of (1)O(2) and the diagnosis of superficial tumors.

Superoxide activates constitutive nitric oxide synthase in a brain particulate fraction

Nitric oxide (*NO) can act as an antioxidant by directly scavenging reactive free radicals, inhibiting the oxidative chemistry of iron, and signaling the up-regulation of antioxidant enzymes. However, the cellular utility of *NO as an antioxidant requires that constitutive nitric oxide synthase (NOS) be activated rapidly by a signal(s) for oxidant formation. We report here that superoxide (O2*-), added directly as potassium superoxide (KO2), produced a superoxide dismutase-sensitive and hydrogen peroxide-independent stimulation of NOS activity, measured by the conversion of [3H]arginine to [3H]citrulline and nitrite formation, in a synaptic particulate fraction from rat brain cerebral cortex. O2*- produced maximal activation of NOS in the presence of the antioxidant urate and ATP. Stimulation of NOS activity by O2*- was abolished by N-monomethyl-L-arginine and by the Ca2+ chelator EGTA but not by 7-nitroindazole, which would be expected to inhibit neuronal NOS. We propose that limited activation of NOS by O2*- may be an important contributor to brain oxidant defenses and, more generally, a signal for cellular adaptation and survival, although excessive generation of nitrogen oxides would be expected to produce neurotoxicity.

Hydroxyl radical generation: the effect of bicarbonate, dioxygen and buffer concentration on pH-dependent chemiluminescence

Enhanced chemiluminescence (CL) induced by HO* was detected using the primary enhancers luminol (Lum), isoluminol (ILum) and lucigenin (Luc), in the absence of HCO3-, at pH 9.5, 10.0 and 10.5 but not between pH 4.0 and 9.0. This was confirmed using nine different HO* generators. FeCl3/NTA/H2O2 was the only HO* generator that was able to generate singular HO* which was obtained entirely from the Fenton reaction. However, this was so only at pH 10.0 since at all other pHs multiple ROS were produced. This was confirmed by the chemical detection of the fluorescent hydroxylated product of terephthalic acid in the absence of O2. No HO* Lum-CL pH optima coincided with the O2*- mediated Lum-CL optima found at pH 8.0 and 9.0. Bicarbonate had an enhancing effect on Lum-CL which was 70-2700% at pH 10.0 for the different HO* generators. This was due to the conversion of the radical-electron from HO* to CO3*-, making CL detection more efficient since less HO* were lost initially before detection. Methyl-cypridine-luciferin analogue (MCLA) elicited CL in the pH range 4.0-10.0 with the same set of generators in the absence of HCO3-. The iron-containing generators had their different MCLA-CL optima at pH 4.5, 5.0 or 6.0, excluding those overlapping with the O2(*-)-mediated CL optima. The two copper-containing generators had optima at the same pHs, viz, 7.0 and 10.5. Again, FeCl3/NTA/H2O2 was the only HO* generator able to produce singular HO* by the Fenton reaction. However, whereas Lum-CL was able to detect singular HO* only at pH 10.0, MCLA-CL detected it at pH 5.0 and 5.5. Therefore, MCLA is the most suitable CL enhancer for physiological assessments since it is the most sensitive enhancer and has HO* CL optima nearer to physiological pH than the other probes. The HCO3- enhancement of MCLA-CL was even greater than that of Lum-CL, since increases of 114-fold and 37-fold, respectively, were obtained at these HO*-specific pH optima for FeCl3/NTA/H2O2. Therefore, bicarbonate concentration is as important a parameter as pH when the enhanced CL of a non-cellular system is determined. Hydrogen peroxide was not able to elicit CL directly but, due to trace metal contamination, it produced artifactual CL due to HO* formation. High H2O2 levels, which prevent spontaneous O2*- dismutation, helped to establish the overlapping pH optima of CL mediated by O2*- and HO* which were artifactually produced either by O2*- via H2O2 and trace metals or by perferryl intermediates, respectively. Due to spontaneous dismutation to H2O2, only 22% of the O2*- produced by HX/XO could be detected by enhanced CL.

Quenching of singlet oxygen by carotenoids produced in escherichia coli - attenuation of singlet oxygen-mediated bacterial killing by carotenoids

We examined the viability of Escherichia coli transformants harboring various carotenoids synthesizing genes in a medium containing an enzymatic singlet oxygen generating system, which contained myeloperoxidase, hydrogen peroxide and Br(-) at pH 4.5. Singlet oxygen quenching activities of various carotenoids in phosphatidyl choline micelles in aqueous media were also studied using the same enzymatic singlet oxygen generating system. Viability of the transformants producing carotenoids was higher than that of the wild type E. coli in the singlet oxygen generation mixture. Of the transformants tested, the viability of zeaxanthin-diglucoside producing transformant was the highest. Carotenoids in increasing order of k(q) values were beta-carotene, a cyclic carotene<zeaxanthin with hydroxy groups < or =lycopene, an acyclic carotene<canthaxanthin and astaxanthin with keto groups <<zeaxanthin-diglucoside. The k(q) value of zeaxanthin-diglucoside was 3.5 times higher than that of beta-carotene. These results suggest that orientation of the carotenoids in lipid layers of micelles and also in phospholipid membrane of bacteria is important for quenching of singlet oxygen. Furthermore, the viability of transformants producing lycopene and phytoene was almost as high as that of the transformant producing zeaxanthin-glucoside.

Antioxidants suitable for use with chemiluminescence to identify oxyradical species

From a panel of 24 alleged antioxidants the most suitable antioxidants (AO) for use with chemiluminescence (CL) experiments were determined. Superoxide dismutase (SOD), using luminol as the chemiluminescence probe (Lum-CL), was inhibitory only towards O2*- and not HO* or (1)O2. SOD was thus a suitable antioxidant for O2*-, as was tiron. Tiron had advantages, however, since SOD acted as a pro-oxidant in the presence of H2O2 or H2O2/HO* generators. The two most suitable antioxidants for (1)O2 were diphenylisobenzofuran (DBF) and tryptophan, for both Lum and Lucigenin-CL (Luc-CL). Desferrioxamine, with both Lum and Luc-CL, was a very effective scavenger for HO*, but appeared to be an even more effective scavenger for (1)O2. Cysteamine showed the best discrimination between IC50s when the two (1)O2 generators NaOCl/H2O2 and NDPO2 were compared. Cysteamine was, therefore, the only scavenger that was appropriate for studies with hypochlorite. Melatonin, with Lum-CL, was found to be the most suitable scavenger for HO*. Mannitol, the classical AO for HO*, was not suitable when used with CL since it acted as a pro-oxidant. Some of the AOs revealed either calyx- or bell-shaped CL inhibition profiles and presumably, therefore, may act as both pro- or antioxidants at different concentrations. Antioxidants showing these kinds of dual activities should be used with caution in CL studies.

Chemiluminescent detection and imaging of reactive oxygen species in live mouse skin exposed to UVA

The recent increase of ultraviolet (UV) rays on Earth due to the increasing size of the ozone hole is suggested to be harmful to life and to accelerate premature photoaging of the skin. The detrimental effects of UV radiation on the skin are associated with the generation of reactive oxygen species (ROS) such as superoxide anion radical (*O(-)(2)), hydrogen peroxide (H(2)O(2)), hydroxyl radical (*OH), and singlet oxygen ((1)O(2)). However, direct proof of such ROS produced in the skin under UV irradiation has been elusive. In this study, we report first in vivo detection and imaging of the generated ROS in the skin of live mice following UVA irradiation, in which both a sensitive and specific chemiluminescence probe (CLA) and an ultralow-light-imaging apparatus with a CCD camera were used. In addition, we found that *O(-)(2) is formed spontaneously and (1)O(2) is generated in the UVA-irradiated skin. This method should be useful not only for noninvasive investigation of the spatial distribution and quantitative determination of ROS in the skin of live animals, but also for in vivo evaluation of the protective ability of free radical scavengers and antioxidants.

Detection of active oxygen species in biological systems

1. Cypridina luciferin analogues, 2-methyl-6-(p-methoxyphenyl)-3,7- dihydroimidazo[1,2-a]pyrazin-3-one (MCLD) and 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one(CLA ), react with O2- or 1O2 to emit light in visible region. Such chemiluminescences were used for the detection of O2- or 1O2 in activated leukocyte systems and myeloperoxidase (granulocyte-extract) + Br- + H2O2 systems in vitro. 2. The mechanisms of MCLA (CLA)-dependent luminescence is described in detail. Superoxide generated from sinusoidal cells in acute ethanol intoxication of rats was detected by MCLA-dependent luminescence from the surface of perfused rat liver (organ luminescence). 3. Furthermore, with alive animals, O2- generated in the lung of rats with necrotized pancreatitis and that in the stomach of rats after ischemia/reperfusion were detected by their organ luminescences.

Coelenterazine analogs as chemiluminescent probe for superoxide anion

Eleven new coelenterazine analogs containing the 3,7-dihydroimidazo[1,2-alpha]pyrazin-3-one structure were synthesized. The superoxide-triggered chemiluminescence of these compounds was investigated using the hypoxanthine-xanthine oxidase system in comparison with four known compounds. The results showed that an alkyl substitution at the position 5 of the imidazopyrazinone ring causes a drastic decrease in the superoxide-dependent chemiluminescence intensity, whereas a dimethylene bridge added between the position 5 and the phenyl group bound to the position 6 dramatically increases the luminescence intensity, indicating the potential usefulness of this type of compound as a probe for superoxide anion. The luminescence intensity of the bridged analog was 33 times greater than that of MCLA [2-methyl-6-(4-methoxyphenyl)-3, 7-dihydroimidazo[1,2-alpha]pyrazin-3-one], the most sensitive superoxide probe of Cypridina luciferin-type. Two of the analogs synthesized, each with a covalently bound cyclodextrin, had a good solubility in water, an advantage in actual use. Moreover, one of them having a beta-cyclodextrin group showed a unique property; its luminescence was little affected by various substances in the environment.

Improved preparation of leukocytes for chemiluminescent study of human phagocytic leukocyte-generated reactive oxygen species

Leukocyte oxidative function was investigated in a more physiological milieu than currently used in the chemiluminescence (CL) technique. Heparinized blood was mixed with 6% dextran-T70 (9:1) and the leukocyte-rich plasma obtained without centrifugation was used for the CL experiments (phagocyte count was adjusted to 0.7 x 10(6)/mL with Hanks' buffer) (method A). In this medium, phagocytes responded to stimulation by opsonized zymosan, producing strong luminescence in the presence of 0.5 mumol/L MCLA. CL was inhibited by superoxide dismutase, suggesting that the luminescence reaction was attributable to O2-. Granulocytes were also prepared by the usual method involving centrifugation and were then suspended in plasma (method B). Oxidative function of phagocytes prepared by the two methods was studied together with whole blood as aliquots diluted with Hanks' buffer up to a factor of 1000. Luminescence reached a peak value at a dilution factor of 16, but at very high dilutions luminescence decreased sharply. Significantly higher luminescence values were obtained with samples from method A. Luminescence of whole blood peaked at a dilution factor of 248 but it was less than the value obtained using samples prepared by method A or B. As samples prepared by method A contain all the leukocyte populations, platelets, residual red cells and plasma proteins, the assay of leukocyte-generated reactive oxygens using CL is attained in more physiological conditions than method B in which leukocytes may be damaged owing to repeated centrifugation and hypotonic shock.

A high involvement of O2- possibly generated in inner membranes for iron-induced microsomal lipid peroxidation

The lipid peroxidation of and the O2- generation by rat liver microsomes in the presence of NADPH or both NADPH and Fe3+ were determined by thiobarbituric acid-reacting substance formation and by chemiluminescence intensities with a cypridina luciferin analog, 2-methyl-6-(p-methoxyphenyl)-3, 7-dihydroimidazo[1,2-a]pyrazin-3-one(MCLA), as a chemiluminescence probe. Judging from the experiments with various inhibitors on the O2- generation and the lipid peroxidation, O2- generated, at intramembranous site, by cytochrome P-450 system is considered to be highly involved in the iron-induced lipid peroxidation.

Highly sensitive chemiluminescence method for determining myeloperoxidase in human polymorphonuclear leukocytes

Myeloperoxidase activity was assayed by a chemiluminescence method, using a cypridina luciferin analog as a chemiluminescence probe, after extraction from peripheral human polymorphonuclear leukocytes. The chemiluminescence method was based on the detection of 1O2 generated by myeloperoxidase-catalyzed HOBr formation followed by the interaction of HOBr with H2O2 at pH 4.5. With this method, myeloperoxidase in less than 100 polymorphonuclear leukocytes could be detected and myeloperoxidase in 10(6) polymorphonuclear leukocytes would be calculated to be 14.4 pmol. Eosinophil extract, which contains eosinophil peroxidase, catalyzed 1O2 generation to a great extent, compared with the polymorphonuclear leukocyte extract at pH 4.5. Myeloperoxidase activity in extract of neutrophil fraction could be greatly influenced by eosinophil contamination.