A new purification procedure for bovine milk xanthine oxidase: effect of proteolysis on the subunit structure

A Versatile Toolkit for Controllable and Highly Selective Multifunctionalization of Bacterial Magnetic Nanoparticles

Their unique material characteristics, i.e. high crystallinity, strong magnetization, uniform shape and size, and the ability to engineer the enveloping membrane in vivo make bacterial magnetosomes highly interesting for many biomedical and biotechnological applications. In this study, a versatile toolkit is developed for the multifunctionalization of magnetic nanoparticles in the magnetotactic bacterium Magnetospirillum gryphiswaldense, and the use of several abundant magnetosome membrane proteins as anchors for functional moieties is explored. High-level magnetosome display of cargo proteins enables the generation of engineered nanoparticles with several genetically encoded functionalities, including a core-shell structure, magnetization, two different catalytic activities, fluorescence and the presence of a versatile connector that allows the incorporation into a hydrogel-based matrix by specific coupling reactions. The resulting reusable magnetic composite demonstrates the high potential of synthetic biology for the production of multifunctional nanomaterials, turning the magnetosome surface into a platform for specific versatile display of functional moieties.

RTP801 Amplifies Nicotinamide Adenine Dinucleotide Phosphate Oxidase-4-Dependent Oxidative Stress Induced by Cigarette Smoke

Tobacco smoke (TS) causes chronic obstructive pulmonary disease, including chronic bronchitis, emphysema, and asthma. Rtp801, an inhibitor of mechanistic target of rapamycin, is induced by oxidative stress triggered by TS. Its up-regulation drives lung susceptibility to TS injury by enhancing inflammation and alveolar destruction. We postulated that Rtp801 is not only increased by reactive oxygen species (ROS) in TS but also instrumental in creating a feedforward process leading to amplification of endogenous ROS generation. We used cigarette smoke extract (CSE) to model the effect of TS in wild-type (Wt) and knockout (KO-Rtp801) mouse lung fibroblasts (MLF). The production of superoxide anion in KO-Rtp801 MLF was lower than that in Rtp801 Wt cells after CSE treatment, and it was inhibited in Wt MLF by silencing nicotinamide adenine dinucleotide phosphate oxidase-4 (Nox4) expression with small interfering Nox4 RNA. We observed a cytoplasmic location of ROS formation by real-time redox changes using reduction-oxidation-sensitive green fluorescent protein profluorescent probes. Both the superoxide production and the increase in the cytoplasmic redox were inhibited by apocynin. Reduction in the activity of Sod and decreases in the expression of Sod2 and Gpx1 genes were associated with Rtp801 CSE induction. The ROS produced by Nox4 in conjunction with the decrease in cellular antioxidant enzymatic defenses may account for the observed cytoplasmic redox changes and cellular damage caused by TS.

Xanthine Oxidase: Isolation, Assays of Activity, and Inhibition

Xanthine oxidase (XO) is an important enzyme catalyzing the hydroxylation of hypoxanthine to xanthine and xanthine to uric acid which is excreted by kidneys. Excessive production and/or inadequate excretion of uric acid results in hyperuricemia. This paper presents a detailed review of methods of isolation, determination of xanthine oxidase activity, and the effect of plant extracts and their constituents on it. Determining the content and activities of XO can be used for diagnostic purposes. Testing inhibition of XO is important for detection of potentially effective compounds or extracts that can be used to treat diseases that are caused by increased activity of XO.In vitrobioassays are used to examine test material for XO inhibition, as inhibitors of XO may be potentially useful for the treatment of gout or other XO induced diseases. Several authors reported on the XO inhibitory potential of traditionally used medicinal plants.

Analysis of superoxide dismutase activity

Measuring the activity of superoxide dismutases (SODs), the enzymes responsible for maintaining the steady state level of hydrogen peroxide, is challenging because the substrate is unstable at physiological pH and it reacts with itself. Fortunately the rate of reaction with dismutase is far greater than the rate of self reaction. As described in this unit, this activity can be measured indirectly based on competition between SOD and an indicator molecule that reacts avidly with superoxide to produce a measurable change in absorption, thus it is possible to measure total SOD activity or that of CuZn-SOD and MnSOD. The activity can also be measured by an activity stain applied to thin-film agarose or native polyacrylamide gels.

Hydrogen peroxide is the major oxidant product of xanthine oxidase

Xanthine oxidase (XO) is a critical source of reactive oxygen species (ROS) in inflammatory disease. Focus, however, has centered almost exclusively on XO-derived superoxide (O(2)(*-)), whereas direct H(2)O(2) production from XO has been less well investigated. Therefore, we examined the relative quantities of O(2)(*-) and H(2)O(2) produced by XO under a range (1-21%) of O(2) tensions. At O(2) concentrations between 10 and 21%, H(2)O(2) accounted for approximately 75% of ROS production. As O(2) concentrations were lowered, there was a concentration-dependent increase in H(2)O(2) formation, accounting for 90% of ROS production at 1% O(2). Alterations in pH between 5.5 and 7.4 did not affect the relative proportions of H(2)O(2) and O(2)(*-) formation. Immobilization of XO, by binding to heparin-Sepharose, further enhanced relative H(2)O(2) production by approximately 30%, under both normoxic and hypoxic conditions. Furthermore, XO bound to glycosaminoglycans on the apical surface of bovine aortic endothelial cells demonstrated a similar ROS production profile. These data establish H(2)O(2) as the dominant (70-95%) reactive product produced by XO under clinically relevant conditions and emphasize the importance of H(2)O(2) as a critical factor when examining the contributory roles of XO-catalyzed ROS in inflammatory processes as well as cellular signaling.

Nitro-oleic acid, a novel and irreversible inhibitor of xanthine oxidoreductase

Xanthine oxidoreductase (XOR) generates proinflammatory oxidants and secondary nitrating species, with inhibition of XOR proving beneficial in a variety of disorders. Electrophilic nitrated fatty acid derivatives, such as nitro-oleic acid (OA-NO2), display anti-inflammatory effects with pleiotropic properties. Nitro-oleic acid inhibits XOR activity in a concentration-dependent manner with an IC50 of 0.6 microM, limiting both purine oxidation and formation of superoxide (O2.). Enzyme inhibition by OA-NO2 is not reversed by thiol reagents, including glutathione, beta-mercaptoethanol, and dithiothreitol. Structure-function studies indicate that the carboxylic acid moiety, nitration at the 9 or 10 olefinic carbon, and unsaturation is required for XOR inhibition. Enzyme turnover and competitive reactivation studies reveal inhibition of electron transfer reactions at the molybdenum cofactor accounts for OA-NO2-induced inhibition. Importantly, OA-NO2 more potently inhibits cell-associated XOR-dependent O2. production than does allopurinol. Combined, these data establish a novel role for OA-NO2 in the inhibition of XOR-derived oxidant formation.

SOD-like activity of Mn(II) beta-octabromo-meso-tetrakis(N-methylpyridinium-3-yl)porphyrin equals that of the enzyme itself

Mn porphyrins are among the most efficient SOD mimics with potency approaching that of SOD enzymes. The most potent ones, Mn(III) N-alkylpyridylporphyrins bear positive charges in a close proximity to the metal site, affording thermodynamic and kinetic facilitation for the reaction with negatively charged superoxide. The addition of electron-withdrawing bromines onto beta-pyrrolic positions dramatically improves thermodynamic facilitation for the O2*- dismutation. We have previously characterized the para isomer, Mn(II)Br(8)TM-4-PyP(4+) [Mn(II) beta-octabromo-meso-tetrakis(N-methylpyridinium-4-yl)porphyrin]. Herein we fully characterized its meta analogue, Mn(II)Br(8)TM-3-PyP(4+) with respect to UV/vis spectroscopy, electron spray mass spectrometry, electrochemistry, O2*- dismutation, metal-ligand stability, and the ability to protect SOD-deficient Escherichia coli in comparison with its para analogue. The increased electron-deficiency of the metal center stabilizes Mn in its +2 oxidation state. The metal-centered Mn(III)/Mn(II) reduction potential, E((1/2))=+468 mV vs NHE, is increased by 416 mV with respect to non-brominated analogue, Mn(III)TM-3-PyP(5+) and is only 12 mV less positive than for para isomer. Yet, the complex is significantly more stable towards the loss of metal than its para analogue. As expected, based on the structure-activity relationships, an increase in E((1/2)) results in a higher catalytic rate constant for the O2*- dismutation, log k(cat)> or =8.85; 1.5-fold increase with respect to the para isomer. The IC(50) was calculated to be < or =3.7 nM. Manipulation of the electron-deficiency of a cationic porphyrin resulted, therefore, in the highest k(cat) ever reported for a metalloporphyrin, being essentially identical to the k(cat) of superoxide dismutases (log k(cat)=8.84-9.30). The positive kinetic salt effect points to the unexpected, unique and first time recorded behavior of Mn beta-octabrominated porphyrins when compared to other Mn porphyrins studied thus far. When species of opposing charges react, the increase in ionic strength invariably results in the decreased rate constant; with brominated porphyrins the opposite was found to be true. The effect is 3.5-fold greater with meta than with para isomer, which is discussed with respect to the closer proximity of the quaternary nitrogens of the meta isomer to the metal center than that of the para isomer. The potency of Mn(II)Br(8)TM-3-PyP(4+) was corroborated by in vivo studies, where 500 nM allows SOD-deficient E. coli to grow >60% of the growth of wild type; at concentrations > or =5 microM it exhibits toxicity. Our work shows that exceptionally high k(cat) for the O2*- disproportionation can be achieved not only with an N(5)-type coordination motif, as rationalized previously for aza crown ether (cyclic polyamines) complexes, but also with a N(4)-type motif as in the Mn porphyrin case; both motifs sharing "up-down-up-down" steric arrangement.

Impact of electrostatics in redox modulation of oxidative stress by Mn porphyrins: protection of SOD-deficient Escherichia coli via alternative mechanism where Mn porphyrin acts as a Mn carrier

Understanding the factors that determine the ability of Mn porphyrins to scavenge reactive species is essential for tuning their in vivo efficacy. We present herein the revised structure-activity relationships accounting for the critical importance of electrostatics in the Mn porphyrin-based redox modulation systems and show that the design of effective SOD mimics (per se) based on anionic porphyrins is greatly hindered by inappropriate electrostatics. A new strategy for the beta-octabromination of the prototypical anionic Mn porphyrins Mn(III) meso-tetrakis(p-carboxylatophenyl)porphyrin ([Mn(III)TCPP](3-) or MnTBAP(3-)) and Mn(III) meso-tetrakis(p-sulfonatophenyl)porphyrin ([Mn(III)TSPP](3-)), to yield the corresponding anionic analogues [Mn(III)Br(8)TCPP](3-) and [Mn(III)Br(8)TSPP](3-), respectively, is described along with characterization data, stability studies, and their ability to substitute for SOD in SOD-deficient Escherichia coli. Despite the Mn(III)/Mn(II) reduction potential of [Mn(III)Br(8)TCPP](3-) and [Mn(III)Br(8)TSPP](3-) being close to the SOD-enzyme optimum and nearly identical to that of the cationic Mn(III) meso-tetrakis(N-methylpyridinium-2-yl)porphyrin (Mn(III)TM-2-PyP(5+)), the SOD activity of both anionic brominated porphyrins ([Mn(III)Br(8)TCPP](3-), E(1/2)=+213 mV vs NHE, log k(cat)=5.07; [Mn(III)Br(8)TSPP](3-), E(1/2)=+209 mV, log k(cat)=5.56) is considerably lower than that of Mn(III)TM-2-PyP(5+) (E(1/2)=+220 mV, log k(cat)=7.79). This illustrates the impact of electrostatic guidance of O(2)(-) toward the metal center of the mimic. With low k(cat), the [Mn(III)TCPP](3-), [Mn(III)TSPP](3-), and [Mn(III)Br(8)TCPP](3-) did not rescue SOD-deficient E. coli. The striking ability of [Mn(III)Br(8)TSPP](3-) to substitute for the SOD enzymes in the E. coli model does not correlate with its log k(cat). In fact, the protectiveness of [Mn(III)Br(8)TSPP](3-) is comparable to or better than that of the potent SOD mimic Mn(III)TM-2-PyP(5+), even though the dismutation rate constant of the anionic complex is 170-fold smaller. Analyses of the medium and E. coli cell extract revealed that the major species in the [Mn(III)Br(8)TSPP](3-) system is not the Mn complex, but the free-base porphyrin [H(2)Br(8)TSPP](4-) instead. Control experiments with extracellular MnCl(2) showed the lack of E. coli protection, indicating that "free" Mn(2+) cannot enter the cell to a significant extent. We proposed herein the alternative mechanism where a labile Mn porphyrin [Mn(III)Br(8)TSPP](3-) is not an SOD mimic per se but carries Mn into the E. coli cell.

Redox modulation of oxidative stress by Mn porphyrin-based therapeutics: the effect of charge distribution

We evaluate herein the impact of positive charge distribution on the in vitro and in vivo properties of Mn porphyrins as redox modulators possessing the same overall 5+ charge and of minimal stericity demand: Mn(III) meso-tetrakis(trimethylanilinium-4-yl)porphyrin (MnTTriMAP(5+)), Mn(III) meso-tetrakis(N,N'-dimethylpyrazolium-4-yl)porphyrin (MnTDM-4-PzP(5+)), Mn(III) meso-tetrakis(N,N'-dimethylimidazolium-2-yl)porphyrin (MnTDM-2-ImP(5+)), and the ortho and para methylpyridinium complexes Mn(III) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (MnTM-4-PyP(5+)) and Mn(III) meso-tetrakis(N-methylpyridinium-2-yl)porphyrin (MnTM-2-PyP(5+)). Both Mn(III)/Mn(II) reduction potential and SOD activity within the series follow the order: MnTTriMAP(5+)<MnTDM-4-PzP(5+)<MnTM-4-PyP(5+)<MnTM-2-PyP(5+)<MnTDM-2-ImP(5+). The kinetic salt effect (KSE) on the catalytic rate constant for superoxide dismutation (k(cat)) indicates that the electrostatic contribution to the O(2)*(-) dismutation is the greatest with MnTM-2-PyP(5+) and follows the order: MnTM-4-PyP(5+)<MnTDM-4-PzP(5+) approximately MnTDM-2-ImP(5+)<MnTM-2-PyP(5+). The KSE observed on k(cat) suggests that the charges are relatively confined within specific regions of the aryl rings. Whereas the charges in imidazolium, pyrazolium, and MnTM-4-PyP(5+) compounds are distributed in-plane with the porphyrin ring, the charges of MnTM-2-PyP(5+) are either above or below the plane, which channels the negatively-charged superoxide toward the axial positions of the Mn porphyrin more efficiently, and leads to the highest KSE. This mimics the tunneling effect observed in the SOD enzymes themselves. The modulation of the reactivity of the Mn center by the electronic perturbations caused by the meso-aryl substituent could be explained by DFT calculation, whereby a correlation between the Mn(III)/Mn(II) reduction potential (and/or SOD activity) and meso-aryl fragment softness descriptors for nucleophilic (s(f)(+)) and radical (s(f)(o)) attacks was observed. MnTDM-4-PzP(5+) and MnTM-4-PyP(5+) did not protect SOD-deficient E. coli grown aerobically, which is in agreement with their low k(cat). MnTM-2-PyP(5+) and MnTDM-2-ImP(5+) have similar high k(cat), but MnTDM-2-ImP(5+) was significantly less protective to E. coli, probably due to its bulkier size, decreased cellular uptake, and/or observed toxicity. The placement of charges closer to the metal center and spatial charge localization increases both the in vitro and the in vivo SOD activity of the compound.

Antimicrobial properties of milkfat globule membrane fractions

Milkfat globule membranes (MFGMs) were prepared from bovine cream according to standard procedures. These membranes and peptide hydrolysates, which were generated by proteolysis with immobilized digestive enzymes, were screened for antibacterial activity against Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica Typhimurium, Pseudomonas fluorescens, Bacillus cereus, Lactobacillus acidophilus, and Lactobacillus gasseri. Assays were first performed on beef heart infusion (BHI) plates spotted with test protein-peptide fractions and then seeded with lawns of indicator cells to monitor the zone of growth inhibition. Under these experimental conditions, MFGMs were most active against Salmonella Typhimurium and P. fluorescens. However, antibacterial activity was not seen after plating on Luria-Bertani (LB) medium. We determined that the antimicrobial effects observed on BHI plates were due to the generation of H2O2 by xanthine oxidase, a major protein constituent of the MFGMs, as a result of purine catalysis. This substrate is present in BHI but lacking in LB medium. Evaluation of purified xanthine oxidase alone resulted in analogous data trends. The growth of probiotic Lactobacillus strains were affected only marginally when grown on lactobacilli deMan Rogosa Sharpe plates, suggesting the decreased sensitivity of these bacteria to H2O2. In this study, several MFGM hydrolysates exhibited variable antibacterial activity against test food pathogens on agar plates prepared with M9 minimal media, and this variation was not attributable to xanthine oxidase enzymatic activity. The probiotic microorganisms were mostly resilient to these antibacterial fractions. Bovine MFGM fractions may represent an excellent resource material from which to generate native, naturally occurring biodefensive proteins and/or peptides.

Moderate hypoxia induces xanthine oxidoreductase activity in arterial endothelial cells

Xanthine oxidoreductase (XOR) activity has been previously noted to be responsive to changes in O2 tension. While prior studies have focused on the extremes (0-3% and 95-100%) of O2 tensions, we report the influence of 10% O2 on endothelial cell XOR, a concentration resembling modest arterial hypoxia commonly found in patients with chronic cardiopulmonary diseases. Exposure of bovine aortic endothelial cells to 10% O2 increased XOR mRNA and protein abundance by 50%. Concomitantly, there was a 3-fold increase in XOR activity, XOR-dependent reactive oxygen species production, and cellular export of active enzyme. Although increases in mRNA and immunoreactive protein levels were observed, inhibition of transcription, translation, or protein degradation did not significantly alter cellular XOR specific activity, suggesting only modest contributions to 10% O2-induced effects. Exposure to 10% O2 did not increase cellular HIF-1alpha protein levels and hypoxia mimics did not alter XOR activity. Treatment of control cells with adenosine resulted in increased XOR activity similar to hypoxia. Exposure to the adenosine receptor agonist NECA increased enzymatic activity 4-fold while 8SPT, an adenosine receptor antagonist, reduced hypoxic induction of XOR activity approximately 50%. Combined, these data reveal that moderate hypoxia significantly enhances endothelial XOR specific activity, release, and XOR-derived reactive oxygen species generation. These effects appear to be mediated in part via adenosine-dependent processes.

New PEG-ylated Mn(iii) porphyrins approaching catalytic activity of SOD enzyme

Two new tri(ethyleneglycol)-derivatized Mn(III) porphyrins were synthesized with the aim of increasing their bioavailability, and blood-circulating half-life. These are Mn(III) tetrakis(N-(1-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)pyridinium-2-yl)porphyrin, MnTTEG-2-PyP5+ and Mn(III) tetrakis(N,N'-di(1-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)imidazolium-2-yl)porphyrin, MnTDTEG-2-ImP5+. Both porphyrins have ortho pyridyl or di-ortho imidazolyl electron-withdrawing substituents at meso positions of the porphyrin ring that assure highly positive metal centered redox potentials, E1/2 = +250 mV vs. NHE for MnTTEG-2-PyP5+ and E1/2 = + 412 mV vs. NHE for MnTDTEG-2-ImP5+. As expected, from established E1/2 vs. log kcat(O2 *-) structure-activity relationships for metalloporphyrins (Batinic-Haberle et al., Inorg. Chem., 1999, 38, 4011), both compounds exhibit higher SOD-like activity than any meso-substituted Mn(III) porphyrins-based SOD mimic thus far, log kcat = 8.11 (MnTTEG-2-PyP5+) and log kcat = 8.55 (MnTDTEG-2-ImP5+), the former being only a few-fold less potent in disproportionating O2*- than the SOD enzyme itself. The new porphyrins are stable to both acid and EDTA, and non toxic to E. coli. Despite elongated substituents, which could potentially lower their ability to cross the cell wall, MnTTEG-2-PyP5+ and MnTDTEG-2-ImP5+ exhibit similar protection of SOD-deficient E. coli as their much smaller ethyl analogues MnTE-2-PyP5+ and MnTDE-2-ImP5+, respectively. Consequently, with anticipated increased blood-circulating half-life, these new Mn(III) porphyrins may be more effective in ameliorating oxidative stress injuries than ethyl analogues that have been already successfully explored in vivo.

Complementation of SOD-deficient Escherichia coli by manganese porphyrin mimics of superoxide dismutase activity

Cationic Mn(III) porphyrins substituted on the methine bridge carbons (meso positions) with N-alkylpyridinium or N,N'-diethylimidazolium groups have been prepared and characterized, both chemically and as SOD mimics. The ortho tetrakis N-methylpyridinium compound was substantially more active than the corresponding para isomer. This ortho compound also exhibited a more positive redox potential and greater ability to facilitate the aerobic growth of a SOD-deficient Escherichia coli. Analogs with longer alkyl side chains and with methoxyethyl side chains, as well as with N,N'-diethylimidazolium and N,N'-dimethoxyethylimidazolium groups on the meso positions, have been prepared in anticipation of greater penetration of the cells due to greater lipophilicity. We now report that the more lipophilic compounds were effective at complementing the SOD-deficient E. coli at lower concentrations than were needed with the less lipophilic compounds. The greater efficacy of the more lipophilic compounds was achieved at the cost of greater toxicity that became apparent when these compounds were applied at higher concentrations.

Binding of xanthine oxidase to glycosaminoglycans limits inhibition by oxypurinol

Although the binding of xanthine oxidase (XO) to glycosaminoglycans (GAGs) results in significant alterations in its catalytic properties, the consequence of XO/GAG immobilization on interactions with clinically relevant inhibitors is unknown. Thus, the inhibition kinetics of oxypurinol for XO was determined using saturating concentrations of xanthine. When XO was bound to a prototypical GAG, heparin-Sepharose 6B (HS6B-XO), the rate of inactivation for uric acid formation from xanthine was less than that for XO in solution (k(inact) = 0.24 versus 0.39 min(-1)). Additionally, the overall inhibition constant (K(i)) of oxypurinol for HS6B-XO was 2-5-fold greater than for free XO (451 versus 85 nm). Univalent electron flux (O(2)(.) formation) was diminished by the binding of XO to heparin from 28.5% for free XO to 18.7% for GAG-immobilized XO. Similar to the results obtained with HS6B-XO, the binding of XO to bovine aortic endothelial cells rendered the enzyme resistant to inhibition by oxypurinol, achieving approximately 50% inhibition. These results reveal that GAG immobilization of XO in both HS6B and cell models substantially limits oxypurinol inhibition of XO, an event that has important relevance for the use of pyrazolo inhibitors of XO in clinical situations where XO and its products may play a pathogenic role.

New class of potent catalysts of O2.-dismutation. Mn(III) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

Three new Mn(III) porphyrin catalysts of O2.-dismutation (superoxide dismutase mimics), bearing ether oxygen atoms within their side chains, were synthesized and characterized: Mn(III) 5,10,15,20-tetrakis[N-(2-methoxyethyl)pyridinium-2-yl]porphyrin (MnTMOE-2-PyP(5+)), Mn(III)5,10,15,20-tetrakis[N-methyl-N'-(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTM,MOE-2-ImP(5+)) and Mn(III) 5,10,15,20-tetrakis[N,N'-di(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTDMOE-2-ImP(5+)). Their catalytic rate constants for O2.-dismutation (disproportionation) and the related metal-centered redox potentials vs. NHE are: log k(cat)= 8.04 (E(1/2)=+251 mV) for MnTMOE-2-PyP(5+), log k(cat)= 7.98 (E(1/2)=+356 mV) for MnTM,MOE-2-ImP(5+) and log k(cat)= 7.59 (E(1/2)=+365 mV) for MnTDMOE-2-ImP(5+). The new porphyrins were compared to the previously described SOD mimics Mn(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)), Mn(III) 5,10,15,20-tetrakis(N-n-butylpyridinium-2-yl)porphyrin (MnTnBu-2-PyP(5+)) and Mn(III) 5,10,15,20-tetrakis(N,N'-diethylimidazolium-2-yl)porphyrin (MnTDE-2-ImP(5+)). MnTMOE-2-PyP(5+) has side chains of the same length and the same E(1/2), as MnTnBu-2-PyP(5+)(k(cat)= 7.25, E(1/2)=+ 254 mV), yet it is 6-fold more potent a catalyst of O2.-dismutation , presumably due to the presence of the ether oxygen. The log k(cat)vs. E(1/2) relationship for all Mn porphyrin-based SOD mimics thus far studied is discussed. None of the new compounds were toxic to Escherichia coli in the concentration range studied (up to 30 microM), and protected SOD-deficient E. coli in a concentration-dependent manner. At 3 microM levels, the MnTDMOE-2-ImP(5+), bearing an oxygen atom within each of the eight side chains, was the most effective and offered much higher protection than MnTE-2-PyP(5+), while MnTDE-2-ImP(5+) was of very low efficacy.

Recombinant Rhodobacter capsulatus xanthine dehydrogenase, a useful model system for the characterization of protein variants leading to xanthinuria I in humans

Rhodobacter capsulatus xanthine dehydrogenase (XDH) forms an (alphabeta)2 heterotetramer and is highly homologous to homodimeric eukaryotic XDHs. The crystal structures of bovine XDH and R. capsulatus XDH showed that the two proteins have highly similar folds. We have developed an efficient system for the recombinant expression of R. capsulatus XDH in Escherichia coli. The recombinant protein shows spectral features and a range of substrate specificities similar to bovine milk xanthine oxidase. However, R. capsulatus XDH is at least 5 times more active than bovine XDH and, unlike mammalian XDH, does not undergo the conversion to the oxidase form. EPR spectra were obtained for the FeS centers of the enzyme showing an axial signal for FeSI, which is different from that reported for xanthine oxidase. X-ray absorption spectroscopy at the iron and molybdenum K-edge and the tungsten LIII-edge have been used to probe the different metal coordinations of variant forms of the enzyme. Based on a mutation identified in a patient suffering from xanthinuria I, the corresponding arginine 135 was substituted to a cysteine in R. capsulatus XDH, and the protein variant was purified and characterized. Two different forms of XDH-R135C were purified, an active (alphabeta)2 heterotetrameric form and an inactive (alphabeta) heterodimeric form. The active form contains a full complement of redox centers, whereas in the inactive form the FeSI center is likely to be missing.

Electrostatic contribution in the catalysis of O2*- dismutation by superoxide dismutase mimics. MnIIITE-2-PyP5+ versus MnIIIBr8T-2-PyP+

The Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin (Mn(III)TE-2-PyP(5+)) is a potent superoxide dismutase (SOD) mimic in vitro and was beneficial in rodent models of oxidative stress pathologies. Its high activity has been ascribed to both the favorable redox potential of its metal center and to the electrostatic facilitation assured by the four positive charges encircling the metal center. Its comparison with the non-alkylated, singly charged analogue Mn(III) beta-octabromo meso-tetrakis(2-pyridyl)porphyrin (Mn(III)Br(8)T-2-PyP(+)) enabled us to evaluate the electrostatic contribution to the catalysis of O(2)() dismutation. Both compounds exhibit nearly identical metal-centered redox potential for Mn(III)/Mn(II) redox couple: +228 mV for Mn(III)TE-2-PyP(5+) and +219 mV versus NHE for Mn(III)Br(8)T-2-PyP(+). The eight electron-withdrawing beta pyrrolic bromines contribute equally to the redox properties of the parent Mn(III)T-2-PyP(+) as do four quaternized cationic meso ortho pyridyl nitrogens. However, the SOD-like activity of the highly charged Mn(III)TE-2-PyP(5+) is >100-fold higher (log k(cat) = 7.76) than that of the singly charged Mn(III)Br(8)T-2-PyP(+) (log k(cat) = 5.63). The kinetic salt effect showed that the catalytic rate constants of the Mn(III)TE-2-PyP(5+) and of its methyl analogue, Mn(III)TM-2-PyP(5+), are exactly 5-fold more sensitive to ionic strength than is the k(cat) of Mn(III)Br(8)T-2-PyP(+), which parallels the charge ratio of these compounds. Interestingly, only a small effect of ionic strength on the rate constant was found in the case of penta-charged para (Mn(III)TM-4-PyP(5+)) and meta isomers (Mn(III)TM-3-PyP(5+)), indicating that the placement of the positive charges in the close proximity of the metal center (ortho position) is essential for the electrostatic facilitation of O(2)() dismutation.

Rotational isomers of N-alkylpyridylporphyrins and their metal complexes. HPLC separation, (1)H NMR and X-ray structural characterization, electrochemistry, and catalysis of O(2)(.-) disproportionation

Rotational (atropo-) isomers of Mn(III) meso-tetrakis(N-alkylpyridinium-2-yl)porphyrins and corresponding metal-free porphyrin ligands (where alkyl is methyl, ethyl, n-butyl, n-hexyl) and Zn(II) meso-tetrakis(N-methyl(ethyl,n-hexyl)pyridinium-2-yl)porphyrins were separated and isolated by reverse-phase HPLC. The identity of the rotational isomers of metal-free meso-tetrakis(N-methylpyridinium-2-yl)porphyrin was established by (1)H NMR spectra and by the crystal structure of the fastest eluting fraction (R(f) = 7.7%, R(w) = 9.2%, P2(1)/c, Z = 8, a = 14.2846(15) A, b = 22.2158(24) A, c = 29.369(3) A, beta = 95.374(2) degrees ) which, in accordance with (1)H NMR interpretation, proved to be the alphabetaalphabeta isomer. This result, together with elution intensity patterns, was used to identify the fractions of other Mn(III)-porphyrins, Zn(II)-porphyrins, and corresponding metal-free ligands in the series. All of the atropoisomers were inert toward isomerization which was not observable for 30 days at room temperature and reached only 50% in 16 days at 90 degrees C in the case of the Mn(III)-ethyl analogue. However, a complete freeze-dry removal of the mobile phase from the HPLC fractions caused an almost 100% isomerization. The Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin, as a mixture of atropoisomers (AEOL-10113), has been shown to offer protection in oxidative stress injury ascribed to its high reactivity toward superoxide (k(cat) = 5.8 x 10(7) M(-1) s(-1)) as a consequence of its favorable redox potential (E(1/2) = +228 mV vs NHE). In this work, the atropoisomers were found to have similar redox potentials ranging from +240 to +220 mV, to be similarly potent catalysts of O(2)(.-) disproportionation (dismutation), with k(cat) ranging from 5.5 x 10(7) to 6.8 x 10(7) M(-1) s(-1), and not to preferentially bind to biological tissue.

Structural and conformational analysis of the oxidase to dehydrogenase conversion of xanthine oxidoreductase

Xanthine oxidoreductase (XOR) is a 300-kDa homodimer that can exist as an NAD+-dependent dehydrogenase (XD) or as an O2-dependent oxidase (XO) depending on the oxidation state of its cysteine thiols. Both XD and XO undergo limited cleavage by chymotrypsin and trypsin. Trypsin selectively cleaved both enzyme forms at Lys184, while chymotrypsin cleaved XD primarily at Met181 but cleaved XO at Met181 and at Phe560. Chymotrypsin, but not trypsin, cleavage also prevented the reductive conversion of XO to XD; thus the region surrounding Phe560 appears to be important in the interconversion of the two forms. Size exclusion chromatography showed that disulfide bond formation reduced the hydrodynamic volume of the enzyme, and two-dimensional gel electrophoresis of chymotrypsin-digested XO showed significant, disulfide bond-mediated, conformational heterogeneity in the N-terminal third of the enzyme but no evidence of disulfide bonds between the N-terminal and C-terminal regions or between XOR subunits. These results indicate that intrasubunit disulfide bond formation leads to a global conformational change in XOR that results in the exposure of the region surrounding Phe560. Conformational changes within this region in turn appear to play a critical role in the interconversion between the XD and XO forms of the enzyme.

Manganese(III) biliverdin IX dimethyl ester: a powerful catalytic scavenger of superoxide employing the Mn(III)/Mn(IV) redox couple

A manganese(III) complex of biliverdin IX dimethyl ester, (MnIIIBVDME)2, was prepared and characterized by elemental analysis, UV/vis spectroscopy, cyclic voltammetry, chronocoulometry, electrospray mass spectrometry, freezing-point depression, magnetic susceptibility, and catalytic dismuting of superoxide anion (O2.-). In a dimeric conformation each trivalent manganese is bound to four pyrrolic nitrogens of one biliverdin dimethyl ester molecule and to the enolic oxygen of another molecule. This type of coordination stabilizes the +4 metal oxidation state, whereby the +3/+4 redox cycling of the manganese in aqueous medium was found to be at E1/2 = +0.45 V vs NHE. This potential allows the Mn(III)/Mn(IV) couple to efficiently catalyze the dismutation of O2.- with the catalytic rate constant of kcat = 5.0 x 10(7) M-1 s-1 (concentration calculated per manganese) obtained by cytochrome c assay at pH 7.8 and 25 degrees C. The fifth coordination site of the manganese is occupied by an enolic oxygen, which precludes binding of NO., thus enhancing the specificity of the metal center toward O2.-. For the same reason the (MnIIIBVDME)2 is resistant to attack by H2O2. The compound also proved to be an efficient SOD mimic in vivo, facilitating the aerobic growth of SOD-deficient Escherichia coli.

Copper- and zinc-containing superoxide dismutase can act as a superoxide reductase and a superoxide oxidase

The copper- and zinc-containing superoxide dismutase can catalyze the oxidation of ferrocyanide by O(2) as well as the reduction of ferricyanide by O(2). Thus, it can act as a superoxide dismutase (SOD), a superoxide reductase (SOR), and a superoxide oxidase (SOO). The human manganese-containing SOD does not exert SOR or SOO activities with ferrocyanide or ferricyanide as the redox partners. It is possible that some biological reductants can take the place of ferrocyanide and can also interact with human manganese-containing superoxide dismutase, thus making the SOR activity a reality for both SODs. The consequences of this possibility vis à vis H(2)O(2) production, the overproduction of SODs, and the role of copper- and zinc-containing superoxide dismutase mutations in causing familial amyotrophic lateral sclerosis are discussed, as well as the likelihood that the biologically effective SOD mimics, as described to date, actually function as SORs.

Carbon monoxide dehydrogenase activity in Bradyrhizobium japonicum

Bradyrhizobium japonicum strain 110spc4 was capable of chemolithoautotrophic growth with carbon monoxide (CO) as a sole energy and carbon source under aerobic conditions. The enzyme carbon monoxide dehydrogenase (CODH; EC 1.2.99.2) has been purified 21-fold, with a yield of 16% and a specific activity of 58 nmol of CO oxidized/min/mg of protein, by a procedure that involved differential ultracentrifugation, anion-exchange chromatography, hydrophobic interaction chromatography, and gel filtration. The purified enzyme gave a single protein and activity band on nondenaturing polyacrylamide gel electrophoresis and had a molecular mass of 230,000 Da. The 230-kDa enzyme was composed of large (L; 75-kDa), medium (M; 28.4-kDa), and small (S; 17.2-kDa) subunits occurring in heterohexameric (LMS)(2) subunit composition. The 75-kDa polypeptide exhibited immunological cross-reactivity with the large subunit of the CODH of Oligotropha carboxidovorans. The B. japonicum enzyme contained, per mole, 2.29 atoms of Mo, 7.96 atoms of Fe, 7.60 atoms of labile S, and 1.99 mol of flavin. Treatment of the enzyme with iodoacetamide yielded di(carboxamidomethyl)molybdopterin cytosine dinucleotide, identifying molybdopterin cytosine dinucleotide as the organic portion of the B. japonicum CODH molybdenum cofactor. The absorption spectrum of the purified enzyme was characteristic of a molybdenum-containing iron-sulfur flavoprotein.

Cysteines involved in the interconversion between dehydrogenase and oxidase forms of bovine xanthine oxidoreductase

Mammalian xanthine oxidoreductase exists intracellularly in its dehydrogenase form. However, outside of this reducing milieu the enzyme quickly transforms into an oxidase form. Interconversion can be controlled by sulfhydryl reactive reagents, suggesting that disulfide bridging is linked to this phenomenon. The present work identified cysteines involved in the interconversion process. Purified enzyme was subjected to mild reduction with 1,4-dithioerythriol to regain dehydrogenase activity, and the accessible cysteines were labeled with specific radioactive alkylation reagents, iodoacetic acid. This partial alkylation stabilizes the dehydrogenase form, presumable by hindering formation of disulfide bond(s). Six of 38 cysteines were found to be labeled (residues 169, 170, 535, 992, 1317, and 1325). The significance of this labeling of bovine xanthine oxidoreductase is discussed in relation to structural knowledge about the enzyme, and especially by comparison with the AA sequences of avian and invertebrate enzymes, which do not undergo conversion. Cysteines 535 and 992 are the most likely marked residues to be involved in the interconversion, whereas the other cysteines are located too far from the cofactorbinding areas in xanthine oxidoreductase.

A review and proposed nomenclature for major proteins of the milk-fat globule membrane

The characteristics and possible functions of the most abundant proteins associated with the bovine milk-fat globule membrane are reviewed. Under the auspices of the Milk Protein Nomenclature Committee of the ADSA, a revised nomenclature for the major membrane proteins is proposed and discussed in relation to earlier schemes. We recommend that proteins be assigned specific names as they are identified by molecular cloning and sequencing techniques. The practice of identifying proteins according to their Mr, electrophoretic mobility, or staining characteristics should be discontinued, except for uncharacterized proteins. The properties and amino acid sequences of the following proteins are discussed in detail: MUC1, xanthine dehydrogenase/oxidase, CD36, butyrophilin, adipophilin, periodic acid Schiff 6/7 (PAS 6/7), and fatty acid binding protein. In addition, a compilation of less abundant proteins associated with the bovine milk-fat globule membrane is presented.

Mitochondrial antioxidant function is a potential mechanism for organ differences in interleukin-1-mediated tolerance to oxidative injury

BACKGROUND

Pretreatment with interleukin-1 (IL-1) induces resistance to lung injury from hyperoxia exposure and to cardiac dysfunction after ischemia-reperfusion in animal models. In contrast, IL-1 pretreatment did not produce tolerance to ischemia-reperfusion injury and did not seem to alter antioxidant enzyme activities in the kidney. Recently, we determined that mitochondria scavenge superoxide anion via a nonenzymatic mechanism and that this newly identified intracellular antioxidant function was inducible in the lung. Based on these observations, we hypothesized that organ differences after IL-1 pretreatment between the lung and the heart, which become tolerant, and the kidney, which does not become tolerant, were a consequence of differential responses in mitochondrial superoxide scavenging.

METHODS

Rats were given IL-1alpha (50 ng intratracheally, 36 hrs before assay) and lung and kidney mitochondria were isolated. Mitochondrial scavenging of superoxide anion was then determined by using an assay that we developed and published previously. We then tested the effects of IL-1 pretreatment on lung mitochondrial scavenging of superoxide after hyperoxia exposure.

RESULTS

We found that intratracheal administration of IL-1 did not affect lung mitochondrial superoxide scavenging but decreased kidney mitochondrial superoxide scavenging by 75%. In addition, IL-1 pretreatment preserved lung mitochondrial superoxide scavenging in rats exposed to hyperoxia (95% O2 for 24 hours) compared with untreated rats exposed to hyperoxia in which lung mitochondrial superoxide scavenging was decreased by more than 50%.

CONCLUSIONS

We conclude that IL-1 pretreatment has divergent effects on mitochondrial antioxidant function in the lung and the kidney and speculate that this may reflect previously unidentified tissue-specific differences in mitochondrial function during systemic inflammation. This study offers new insights into why the lung, but not the kidney, acquires tolerance to subsequent oxidative injury after IL-1 pretreatment.

Simple, high-yield purification of xanthine oxidase from bovine milk

Xanthine oxidase, a commercially important enzyme with a wide area of application, was extracted from fresh milk, without added preservatives, using toluene and heat. The short purification procedure, with high yield, consisted of extraction, ammonium sulfate fractionation, and DEAE-Sepharose (fast flow) column chromatography. Xanthine oxidase was eluted as a single activity peak from the column using a buffer gradient. The purification fold, specific activity and yield for the purified xanthine oxidase were 328, 10.161 U/mg and 69%, respectively. The enzyme was concentrated by ultrafiltration, although 31% of the activity was lost during concentration, no change in specific activity was observed. Activity and protein gave coincident staining bands on native polyacrylamide gels. The intensity and the number of bands were dependent on the oxidative state(s) of the enzyme; reduction by 2-mercaptoethanol decreased the intensity of the slow-moving bands and increased the intensity of the fastest-moving band. Following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), two major bands (molecular masses of 152 and 131 kDa) were observed, accounting for > or = 95% of xanthine oxidase. Native- and SDS-PAGE showed that the purified xanthine oxidase becomes a heterodimer due to endogenous proteases.

Alcohol-induced breast cancer: a proposed mechanism

Alcohol consumption increases the risk for breast cancer in women by still undefined means. Alcohol metabolism is known to produce reactive oxygen species (ROS), and breast cancer is associated with high levels of hydroxyl radical (*OH) modified DNA, point mutations, single strand nicks, and chromosome rearrangement. Furthermore, ROS modification of DNA can produce the mutations and DNA damage found in breast cancer. Alcohol dehydrogenase (ADH) and xanthine oxidoreductase (XOR) are expressed and regulated in breast tissues and aldehyde oxidase (AOX) may be present as well. Mammary gland XOR is an efficient source of ROS. Recently, hepatic XOR and AOX were found to generate ROS in two ways from alcohol metabolism: by acetaldehyde consumption and by the intrinsic NADH oxidase activity of both XOR and AOX. The data obtained suggests that: (1) expression of ADH and XOR or AOX in breast tissue provides the enzymes that generate ROS; (2) metabolism of alcohol produces acetaldehyde and NADH that can both be substrates for XOR or AOX and thereby result in ROS formation; and (3) ROS generated by XOR or AOX can induce the carcinogenic mutations and DNA damage found in breast cancer. Accumulation of iron coupled with diminished antioxidant defenses in breast tissue with advancing age provide additional support for this hypothesis because both result in elevated ROS damage that may exacerbate the risk for ROS-induced breast cancer.

Lucigenin as mediator of superoxide production: revisited

Lucigenin caused a concentration-dependent increase in superoxide production by xanthine oxidase plus xanthine. This was seen, in terms of superoxide dismutase-inhibitable reduction of cytochrome c; in spite of the ability of univalently reduced lucigenin to directly reduce cytochrome c. It follows that in the absence of this interference, by the cytochrome, an even greater increase in superoxide production mediated by lucigenin would have been observed. Clearly lucigenin luminescence should not be relied upon as a method for measurement of, or even for detection of, superoxide.

The ortho effect makes manganese(III) meso-tetrakis(N-methylpyridinium-2-yl)porphyrin a powerful and potentially useful superoxide dismutase mimic

The ortho, meta, and para isomers of manganese(III) 5,10,15, 20-tetrakis(N-methylpyridyl)porphyrin, MnTM-2-PyP5+, MnTM-3-PyP5+, and MnTM-4-PyP5+, respectively, were analyzed in terms of their superoxide dismutase (SOD) activity in vitro and in vivo. The impact of their interaction with DNA and RNA on the SOD activity in vivo and in vitro has also been analyzed. Differences in their behavior are due to the combined steric and electrostatic factors. In vitro catalytic activities are closely related to their redox potentials. The half-wave potentials (E1/2) are +0.220 mV, +0.052 mV, and +0.060 V versus normal hydrogen electrode, whereas the rates of dismutation (kcat) are 6.0 x 10(7), 4.1 x 10(6), and 3.8 x 10(6) M-1 s-1 for the ortho, meta, and para isomers, respectively. However, the in vitro activity is not a sufficient predictor of in vivo efficacy. The ortho and meta isomers, although of significantly different in vitro SOD activities, have fairly close in vivo SOD efficacy due to their similarly weak interactions with DNA. In contrast, due to a higher degree of interaction with DNA, the para isomer inhibited growth of SOD-deficient Escherichia coli.

Solubilization and purification of xanthine oxidase from bovine milk fat globule membrane

Bovine milk xanthine oxidase (XO) was isolated and purified from milk fat globule membrane (MFGM). The method included the following steps: solubilization of XO from MFGM in 200 mM dithiothreitol (DTT) at pH 8.0, fractionation of solubilized proteins with ammonium sulfate, chromatography on DEAE-Sepharose with gradient elution, and rechromatography of the XO fraction for final purification. The method is highly reproducible, is comparatively simple, and provides highly pure enzyme. Purified XO, analyzed by (8%) SDS-PAGE, had only one band of 140-150 kDa. XO showed a high specific activity of 2.5 units/mg of protein and an A280: A450 ratio of 4.8.

A simple and sensitive method for the activity staining of xanthine oxidase

Xanthine oxidase is a commercially-important enzyme. Several biochemical compounds have been quantitated by xanthine oxidase. Xanthine oxidase has been used as an auxiliary enzyme in the staining of several enzymes or tissues, however, there is no direct staining method available for it, on polyacrylamide gels. Partially-purified xanthine oxidase from cow milk was used as the enzyme source for the development of an activity-staining method on polyacrylamide gels. Staining was very sensitive. Detection of 0.02 microU of the enzyme on polyacrylamide gels was possible. Staining of 0.05 microU takes about 1 min whereas staining of 0.5 microU will take less than 5 s. Addition of TEMED is not essential for activity staining but it did increase both the rate and the intensity of the staining. The stained gels must be washed with distilled water, extensively, in order to remove excess unoxidized nitroblue tetrazolium, and must be protected from light, for a clear background and sharp activity-band staining. This method might be useful for quality control of xanthine oxidase obtained from different sources.

Biochemical characterization of selenium-containing catalytic antibody as a cytosolic glutathione peroxidase mimic

A selenium-containing catalytic antibody (Se-4A4), prepared by converting reactive serine residues of a monoclonal antibody (4A4) raised against a GSH derivative into selenocysteines, acts as a mimic of cytosolic glutathione peroxidase (cGPX). To clarify the mechanism of action of this catalytic antibody, detailed studies on kinetic behaviour and biological activity were carried out. A rate of acceleration (kcat/Km/kuncat) 10(7)-fold that of the uncatalytic reaction is observed. Under similar conditions, the turnover number (kcat) of Se-4A4 is 42% of that of the natural rabbit liver cGPX. The Se-4A4 reaction involves a Ping Pong mechanism, which is the same as that of the natural cGPX. The selenocysteine residue is located in the binding site of the antibody and is shown to be crucial for this activity. Of the thiol compounds tested, only GSH is able to serve as substrate for Se-4A4. It was demonstrated, using the free-radical-damage system (hypoxanthine/xanthine oxidase) of cardiac mitochondria, that Se-4A4 can protect mitochondria from free-radical damage at least 10(4)-fold more effectively than the natural cGPX.

The familial amyotrophic lateral sclerosis-associated amino acid substitutions E100G, G93A, and G93R do not influence the rate of inactivation of copper- and zinc-containing superoxide dismutase by H2O2

Inactivation of copper- and zinc-containing superoxide dismutase (Cu,ZnSOD) by H2O2 is the consequence of several sequential reactions: reduction of the active site Cu(II) to Cu(I) by H2O2; oxidation of the Cu(I) by a second H2O2, thus generating a powerful oxidant, which may be Cu(I)O or Cu(II)OH or Cu(III); and finally oxidation of one of the histidines in the ligand field, causing loss of SOD activity. Three familial amyotrophic lateral sclerosis (FALS)-associated mutant Cu,ZnSODs, i.e., E100G, G93A, and G93R, did not differ from the control enzyme in susceptibility to inactivation by H2O2. It thus appears that an increased peroxidase activity of the FALS-associated Cu,ZnSOD variants might not be a factor in the development of this disease. This leaves the loss of Zn, and the consequent increase in peroxidase activity, or in nitration activity, as a viable explanation (J. P. Crow et al., 1997, J. Neurochem. 69, 1936-1944), among other possibilities.

A mechanism for complementation of the sodA sodB defect in Escherichia coli by overproduction of the rbo gene product (desulfoferrodoxin) from Desulfoarculus baarsii

Overexpression of rbo in Escherichia coli prevents the inactivation of the [4Fe-4S]-containing fumarases that otherwise occurs in the sodA sodB strain. It similarly protects against the increased sensitivity toward H2O2, which is imposed by the lack of SOD A and SOD B. These results would be explained on the basis of scavenging of O-2 within the cells by RBO. This interpretation was supported by measurements of intracellular scavenging of O-2 by the lucigenin luminescence method. Since SOD activity could not be detected in dilute extracts, of the RBO-overexpressing sodA sodB strain, we propose that RBO catalyzes the reduction of O-2 at the expense of cellular reductants such as NAD(P)H. A similar mechanism may apply to other instances of complementation of SOD defects by non-SOD genes.

A potent superoxide dismutase mimic: manganese beta-octabromo-meso-tetrakis-(N-methylpyridinium-4-yl) porphyrin

Variously modified metalloporphyrins offer a promising route to stable and active mimics of superoxide dismutase (SOD). Here we explore bromination on the pyrroles as a means of increasing the redox potentials and the catalytic activities of the copper and manganese complexes of a cationic porphyrin. Mn(II) and Cu(II) octabrominated 5,10,15,20-tetrakis-(N-methylpyridinium-4-yl) porphyrin, Mn(II)OBTMPyP4+, and Cu(II)OBTMPyP4+ were prepared and characterized. The rate constants for the porphyrin-catalyzed dismutation of O2.- as determined from the inhibition of the cytochrome c reduction are k(cat) = 2.2 x 10(8) and 2.9 x 10(6) M(-1) s(-1), i.e., IC50 was calculated to be 12 nM and 0.88 microM, respectively. The metal-centered half-wave potential was E(1/2) = +0.48 V vs NHE for the manganese compound. Cu(II)OBTMPyP4+ proved to be extremely stable, while its Mn(II) analog has a moderate stability, log K = 8.08. Nevertheless, slow manganese dissociation from Mn(II)OBTMPyP4+ enabled the complex to persist and exhibit catalytic activity even at the nanomolar concentration level and at biological pH. The corresponding Mn(III)OBTMPyP5+ complex exhibited significantly increased stability, i.e., demetallation was not detected in the presence of a 400-fold molar excess of EDTA at micromolar porphyrin concentration and at pH 7.8. The beta-substituted manganese porphyrin facilitated the growth of a SOD-deficient strain of Escherichia coli when present at 0.05 microM but was toxic at 1.0 microM. The synthetic approach used in the case of manganese and copper compounds offers numerous possibilities whereby the interplay of the type and of the number of beta substituents on the porphyrin ring would hopefully lead to porphyrin compounds of increased stability, catalytic activity, and decreased toxicity.

Lucigenin luminescence as a measure of intracellular superoxide dismutase activity in Escherichia coli

Lucigenin and paraquat are similar in that each can be taken into Escherichia coli and can then mediate O2.- production by cycles of univalent reduction, to the corresponding monocation radical, followed by autoxidation. Thus, both compounds caused induction of enzymes that are regulated by the soxRS regulon. The lucigenin cation radical has the added property of reacting with O2.-, in a radical-radical addition, to yield an unstable dioxetane, whose decomposition yields light. Superoxide dismutases (SOD), by decreasing [O2.-], inhibit light production and to the same degree inhibit other O2.(-)-dependent reactions in the cell. Lucigenin luminescence was used to show that the levels of SOD in the parental strain provide approximately 95% protection of all O2.(-)-sensitive targets in E. coli. This degree of protection was so close to the limit of 100% that halving the parental level of [SOD], or increasing it 5-fold, had only marginal effects on the intensity of lucigenin-dependent luminescence.

A new irreversibly inhibited form of xanthine oxidase from ethylisonitrile

The treatment of xanthine oxidase with ethylisonitrile results in irreversible inhibition of the catalytic activity. Chemical and spectroscopic evidence suggests that the inhibited enzyme is a new distinct derivative in which the essential sulfido ligand to molybdenum has been modified or removed.

Stage specific expression of milk fat globule membrane glycoproteins in mouse mammary gland: comparison of MFG-E8, butyrophilin, and CD36 with a major milk protein, beta-casein

The expression of mouse milk fat globule membrane (MFGM) glycoproteins, MFG-E8, butyrophilin, CD36 was analyzed by Northern blot analyses. MFG-E8 and butyrophilin mRNAs were specifically detected in the mammary gland of lactating mice, whereas CD36 mRNA was detected in the heart and lung as well as in the mammary gland of lactating mice. The mRNAs of the three MFGM glycoproteins accumulated at mid-lactation were about 2-10-times as much as those of the early and late gestation stages, whereas beta-casein mRNA accumulation was dramatically increased; the mRNA at mid-lactation was no less than 40-times as much as that before lactation. In mouse mammary epithelial cell lines, HC11 and COMMA-1D, only a slight or almost no enhancement for the expression of MFG-E8, butyrophilin and CD36 mRNAs was induced simply by the treatment with the lactogenic hormones such as prolactin, insulin and dexamethasone, whereas the beta-casein mRNA expression was remarkably enhanced only by that treatment. Furthermore, while the beta-casein protein was constantly detected in milk throughout the lactation stage, the content of MFG-E8 and butyrophilin proteins increased during the lactation with an increase in the milk fat content. These results suggest that the stage-specific expression of milk fat globule membrane glycoproteins in mammary epithelial cells is regulated in a similar but not necessarily identical mechanism to that of a major milk protein, beta-casein.

Xanthine oxidase binding to glycosaminoglycans: kinetics and superoxide dismutase interactions of immobilized xanthine oxidase-heparin complexes

Xanthine oxidoreductase (XDH + XO, EC 1.2.3.2) is released into the circulation from organs rich in XO activity. Herein we report the specific high affinity binding of XO to glycosaminoglycans (GAGs) and the preferential association of XO with heparin, compared with heparan sulfate, chondroitin sulfate, and dematan sulfate. The binding of XO to Sepharose 6B-conjugated heparin (HS6B) occurs at physiological ionic strength and increased with pH, with Scatchard analysis revealing a nonlinear binding pattern at pH 7.4. The dissociation constant (Kd) for XO binding was 0.4 to 1.8 x 10(-7) M, similar to the heparin-reversible binding of lipoprotein lipase to vascular endothelium. The binding energy of 9-13 kcal/mol was concordant with noncovalent electrostatic interactions. Xanthine oxidase immobilization to HS6B rendered a catalytically active enzyme from that had kinetic characteristics distinct from XO in free solution. While the Km and Ki for xanthine in phosphate buffer at pH 7.4 were 3 microM and 1.6 mM, respectively, for free XO, they were 15 microM and 2.8 mM for immobilized XO. Inhibition constants for guanine and uric acid were also increased upon XO binding to HS6B. Changes in kinetic parameters were related to a real and not apparent decrease in binding affinity for substrate and inhibitors and were not due to diffusion-controlled processes within the gel matrix. Changes in Km and Ki for xanthine also had a significant influence on the relative quantities of O2.- and H2O2 generated by a given substrate concentration. Superoxide formed by HS6B-bound XO was partially consumed within the gel microenvironment which electrostatically excluded CuZn SOD. Immobilization of XO increased the half-life of enzyme activity in buffer and in the absence of substrate from 67 to 120 h at 4 degrees C. These data indicate that binding to cell surfaces will strongly influence the catalytic properties, oxidant producing capacity, and stability of XO.

Tissue plasminogen activator (tPA) inhibits human neutrophil superoxide anion production in vitro

Because neutrophils contribute to reperfusion injury associated with acute myocardial infarction (MI), and because tissue plasminogen activator (tPA) is often used in the management of MI, we evaluated the effect of tPA on superoxide (O2.-) production by human neutrophils in vitro. We found that adding increasing amounts of tPA significantly (r = 0.89, P < 0.025) and progressively reduced O2.- generation by neutrophils treated with phorbol myristate acetate (PMA) in vitro. Furthermore, adding tPA that had been previously treated with the protease inhibitor, D-Phe-Pro-Arg-chloromethyl ketone HCl (PPACK), also decreased neutrophil O2.- generation in vitro (P < 0.05). In contrast, adding L-arginine, a component of the tPA preparation and a precursor of nitric oxide (NO), did not inhibit PMA-induced neutrophil O2.- production. Also, adding increasing concentrations of tPA did not reduce (P > 0.05) the concentrations of O2.- produced by xanthine oxidase (XO) in vitro. Our findings suggest that tPA reduces neutrophil O2.- generation by a mechanism that is not related to L-arginine, is not dependent on tPA proteolytic activity, and is not a function of direct scavenging. This property may account for some of the effectiveness of tPA in the treatment of MI and/or make tPA valuable for treating acute respiratory distress syndrome (ARDS) or other inflammatory disorders involving neutrophil O2.- production.