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PubMed2000

Redox chemistry in laccase-catalyzed oxidation of N-hydroxy compounds.

1-Hydroxybenzotriazole, violuric acid, and N-hydroxyacetanilide are three N-OH compounds capable of mediating a range of laccase-catalyzed biotransformations, such as paper pulp delignification and degradation of polycyclic hydrocarbons. The mechanism of their enzymatic oxidation was studied with seven fungal laccases. The oxidation had a bell-shaped pH-activity profile with an optimal pH ranging from 4 to 7. The oxidation rate was found to be dependent on the redox potential difference between the N-OH substrate and laccase. A laccase with a higher redox potential or an N-OH compound with a lower redox potential tended to have a higher oxidation rate. Similar to the enzymatic oxidation of phenols, phenoxazines, phenothiazines, and other redox-active compounds, an "outer-sphere" type of single-electron transfer from the substrate to laccase and proton release are speculated to be involved in the rate-limiting step for N-OH oxidation.

Acetaminophen↗
PubMed2004

A study of the spectral and redox properties and covalent flavinylation of the flavoprotein component of p-cresol methylhydroxylase reconstituted with FAD analogues.

The spectral and redox properties are described for the wild-type and Y384F mutant forms of the flavoprotein component (PchF) of flavocytochrome, p-cresol methylhydroxylase (PCMH), and cytochrome-free PchF that harbor FAD analogues. The analogues are iso-FAD (8-demethyl-6-methyl-FAD), 6-amino-FAD (6-NH(2)-FAD), 6-bromo-FAD (6-Br-FAD), 8-nor-8-chloro-FAD (8-Cl-FAD), and 5-deaza-5-carba-FAD (5-deaza-FAD). All of the analogues bound noncovalently and stoichiometrically to cytochrome-free apo-PchF, and the resulting holoproteins had high affinity for the cytochrome subunit, PchC. Noncovalently bound FAD, 6-Br-FAD, or 6-NH(2)-FAD can be induced to bind covalently by exposing holo-PchF to PchC. The rate of this process and the redox potential of the noncovalently bound flavin may be correlated. In addition, the redox potential of each FAD analogue was higher when it was covalently bound than when noncovalently bound to PchF. Furthermore, the potential of a covalently bound or noncovalently bound FAD analogue increased on association of the corresponding holo-PchF with PchC, and the activity increased as the flavin's redox potential increased. It was discovered also that 4-hydroxybenzaldehyde, the final p-cresol oxidation product, is an efficient competitive inhibitor for substrate oxidation by PchF since it binds tightly to this protein when the flavin is oxidized, although it binds more loosely to the enzyme with reduced flavin. Finally, the energies of the charge-transfer bands for the interaction of bound flavin analogues with 4-Br-phenol (a substrate mimic) increased as the potential decreases, although a simple global correlation was not seen. This is the case because the energy is also a function of the redox properties of the bound mimic. The implications of these findings to covalent flavinylation and catalysis are discussed.

Binding Sites↗
PubMed1992

A Pro to His mutation in active site of thioredoxin increases its disulfide-isomerase activity 10-fold. New refolding systems for reduced or randomly oxidized ribonuclease.

Thioredoxin (Trx) from Escherichia coli was compared with bovine protein disulfide-isomerase (PDI) for its ability to catalyze native disulfide formation in either reduced or randomly oxidized (scrambled) ribonuclease A (RNase). On a molar basis, a 100-fold higher concentration of Trx than of PDI was required to give the same rate of native disulfide formation measured as recovery of RNase activity. A Pro-34 to His (P34H Trx) mutation in the active site of E. coli Trx (WCGPC), mimicking the two suggested active sites in PDI (WCGHC), increased the catalytic activity in disulfide formation about 10-fold. The mutant P34H Trx displayed a 35-mV higher redox potential (E'0) of the active site disulfide/dithiol relative to wild type Trx, making it more similar to the redox potential observed for PDI. This higher redox potential correlates well with the enhanced activity and suggests a role for the histidine side chain. Enzymatic isomerization of disulfides in scrambled, oxidized RNase requires the presence of a catalytic thiol such as GSH to initiate the thiol-disulfide interchange. Bovine thioredoxin reductase, together with NADPH, could replace GSH. For oxidative folding of reduced RNase in air with Trx, P34H Trx, or PDI, catalytic amounts of sodium selenite (1 microM) resulted in rapid disulfide formation and high yields of ribonuclease activity equivalent to previously known redox buffers of GSH and GSSG. These results demonstrate no obligatory role for glutathione in disulfide formation. A possible mechanism for the unknown thiol oxidative process accompanying folding and protein disulfide formation in vivo is discussed.

Amino Acid Sequence↗
PubMed1997

Hydrogen bond network in the distal site of peroxidases: spectroscopic properties of Asn70 --> Asp horseradish peroxidase mutant.

The distal His in peroxidases forms a hydrogen bond with the adjacent Asn, which is highly conserved among many plant and fungal peroxidases. Our previous work [Nagano, S., Tanaka, M., Ishimori, K., Watanabe, Y., & Morishima, I. (1996) Biochemistry 35, 14251-14258] has revealed that the replacement of Asn70 in horseradish peroxidase C (HRP) by Val (N70V) and Asp (N70D) discourages the oxidation activity for guaiacol, and the elementary reaction rate constants for the mutants was decreased by 10-15-fold. In order to delineate the structure-function relationship of the His-Asn couple in peroxidase activity, heme environmental structures of the HRP mutant, N70D, were investigated by CD, 1H NMR, and IR spectroscopies as well as Fe2+/Fe3+ redox potential measurements. While N70D mutant exhibited quite similar CD spectra and redox potential to those of native enzyme, the paramagnetic NMR spectrum clearly showed that the hydrogen bond between the distal His and Asp70 is not formed in the mutant. The disappearance of the splitting in the 1H NMR signal of heme peripheral 8-methyl group observed in 50% H2O/50% D2O solution of N70D-CN suggests that the hydrogen bond between the distal His and heme-bound cyanide is also disrupted by the mutation, which was supported by the low C-N vibration frequency and large dissociation constant of the heme-bound cyanide in the mutant. Together with the results from various spectroscopies and redox potentials, we can conclude that the improper positioning of the distal His induced the cleavages of the hydrogen bonds around the distal His, resulting in the substantial decrease of the catalytic activity without large structural alterations of the enzyme. The His-Asn hydrogen bond in the distal site of peroxidases, therefore, is essential for the catalytic activity by controlling the precise location of the distal His.

Asparagine↗
PubMed1990

Autoxidation of oxymyoglobin: a meeting point of the stabilization and the activation of molecular oxygen.

1. The primary events of haemoprotein reactions with molecular oxygen have been re-examined by placing special emphasis upon the reduction properties of dioxygen. 2. In the stepwise reduction of O2 to water via hydrogen peroxide, the addition of the first electron is an unfavourable, uphill process with the midpoint potential of -0.33 V, all the subsequent steps being downhill. This thermodynamic barrier to the first step is, therefore, a most crucial ridge located between the stabilization and the activation of dioxygen performed by haemoproteins. 3. If the proteins have a redox potential much higher than -0.33 V, molecular oxygen must bind to the proteins stably and reversibly. In Mb or Hb, however, the FeO2 centre is always subject to a nucleophilic attack of the water molecule or hydroxyl ion, which can enter the haem pocket from the surrounding solvent. These can cause irreversible oxidation of the FeO2 bonding to the ferric met-form with generation of the superoxide anion. 4. In cases of the oxygen activation, if haemoproteins have a redox potential lower than or close to -0.33 V, the first reduction of O2 to O2- would be a spontaneous process. Cytochrome P-450 provides such an example and can facilitate the subsequent addition of electrons that leads to the breaking of the O-O bond to yield the hydroxylating species. 5. As to the proteins whose redox potential is not facilitative and appreciably higher than -0.33 V, a bimetallic, concerted, two-equivalent reduction of the bound dioxygen to the peroxide level would be much more favoured without the intermediate formation of O2-. This is probably the case of cytochrome c oxidase for the reduction of O2 to water. 6. The redox potential diagrams thus visualize various aspects of the ways haemoproteins overcome their thermodynamic constraints and carry out their specific functions in the stabilization and the activation of molecular oxygen.

Cytochrome P-450 Enzyme System↗
PubMed1997

Elimination of all charged residues in the vicinity of the active-site helix of the disulfide oxidoreductase DsbA. Influence of electrostatic interactions on stability and redox properties.

Disulfide oxidoreductases are structurally related proteins that share the thioredoxin fold and a catalytic disulfide bond that is located at the N terminus of an alpha-helix. The different redox potentials of these enzymes varying from -270 mV for thioredoxin to -125 mV for DsbA have been attributed to the lowered pKa values of their nucleophilic, active-site cysteines and the difference in thermodynamic stability between their oxidized and reduced forms (DeltaDeltaGox/red). The lowered pKa of the nucleophilic cysteine thiols was proposed to result from favorable interactions with the helix dipole and charged residues in their vicinity. In this study, we have eliminated all charged residues in the neighborhood of the active-site disulfide of DsbA from Escherichia coli to analyze their contribution to the physicochemical properties of the protein. We show that the conserved charge network among residues Glu24, Glu37, and Lys58 stabilizes the oxidized form of DsbA and thus does not cause the high redox potential of the enzyme. The pKa values of the nucleophilic cysteine (Cys30) and the redox potentials of the DsbA variants E24Q, E37Q, K58M, E24Q/K58M, E37Q/K58M, E24Q/E37Q, E24Q/E37Q/K58M, and E24Q/E37Q/E38Q/K58M are similar to those of DsbA wild type. The redox potentials of the variants neither correlate with the Cys30 pKa values nor with the DeltaDeltaGox/red values, demonstrating that the relationship between these parameters is far more complex than previously thought.

Amino Acid Sequence↗
PubMed2005

Antioxidant supplements prevent oxidation of cysteine/cystine redox in patients with age-related macular degeneration.

PURPOSE: Determine whether antioxidant supplements alter the plasma glutathione and/or cysteine redox potential in age-related macular degeneration (AMD) patients. DESIGN: This was an ancillary study to the Age-Related Eye Disease Study (AREDS), where subset of AREDS subjects at two sites were studied at two time points, an average of 1.7 and 6.7 years after enrollment. METHODS: Plasma glutathione (GSH), glutathione disulfide (GSSG), cysteine (Cys), and cystine (CySS) were measured by high-performance liquid chromatography, and redox potentials of GSH/GSSG (E(h) GSH) and Cys/CySS (E(h) Cys) were calculated. The means of the metabolites and redox potentials were compared by repeated-measures analysis of variance for subjects receiving antioxidants and those not receiving antioxidants. RESULTS: At the first blood draw, the means for the antioxidant group (n = 153) and no antioxidant group (n = 159) were not significantly different for any of the metabolites or redox potentials. At the second draw, the GSH parameters were not significantly different between the antioxidant (n = 37) and no antioxidant (n = 45) groups; however, mean Cys was significantly higher in the antioxidant group (9.5 vs 7.2 micromol/l, P = .008). Also, mean E(h) Cys was significantly more reduced in the antioxidant group (-74 vs -67.3 mV, P = .03). CONCLUSIONS: The AREDS antioxidant supplements reduced oxidation of E(h) Cys but had no effect on GSH. Because Cys is important for cell growth, apoptosis, and immune function, the beneficial effect of antioxidant supplementation on progression to advanced AMD may be partially explained by its effect on E(h) Cys and/or its effect on Cys availability.

Aged↗
PubMed1999

The effects of pH and semiquinone formation on the oxidation-reduction potentials of flavin mononucleotide. A reappraisal.

Calculation shows that there is poor agreement between frequently cited values for the midpoint redox potentials of the two one-electron steps in the reduction of flavin mononucleotide and equations for the lines that relate these potentials to pH and that use the published pKa values for the three redox states of the flavin [Draper, R. & Ingraham, L.L. (1969) Arch. Biochem. Biophys. 125, 802-808]. Equilibrium data for the first step in the reduction obtained by pulse radiolysis [Anderson, R.F. (1983) Biochim. Biophys. Acta 722, 158-162] show much closer agreement with theory and lead to values for the semiquinone formation constant of flavin mononucleotide that are close to those derived from measurements of the radical concentration using ESR spectroscopy. It is concluded that the data from the second method are more reliable. The redox potentials for flavin mononucleotide at pH 7.0 and 20 degrees C are calculated to be -0.207 V for the overall two-electron reduction (Em), -0.313 V for reduction of the oxidized flavin to the semiquinone (E2) and -0.101 V for the reduction of the semiquinone to the hydroquinone (E1). Information is provided to allow calculation of the three redox potentials at other pH values in the physiological range.

Benzoquinones↗
PubMed1996

Redox control of RNA synthesis in potato mitochondria.

This study shows that the incorporation of radiolabelled UTP into RNA in Percoll-gadient-purified potato mitochondria is regulated by the redox state of the mitochondrial electron transport chain. An early indication that there might be a redox effect on RNA synthesis was a decrease in UTP incorporation in incubates containing an oxidisable substrate, such as succinate or malate. Subsequent use of a variety of electron transport inhibitors acting at different points in the electron transport chain established that the redox state of the Rieske iron-sulphur protein was the major determinant of UTP incorporation. Inhibitors acting on the substrate side of the Rieske iron-sulphur protein, and causing oxidation of components on the oxygen side of their site of action, increased UTP incorporation into RNA. These included antimycin A, myxothiazole, and undecylhydroxydioxobenzothiazole at 500 nM. Inhibitors acting on the oxygen side of the Rieske iron-sulphur protein, and causing a reduction of components on the substrate side of the block, decreased UTP incorporation. These inhibitors were undecylhydroxydioxobenzothiazole at 25 nM and KCN. When phenazine methosulphate was present as an auto-oxidisable electron sink the effect of KCN was diminished. The conclusion from the inhibitor experiments that the redox state of the Rieske iron-suphur protein was important was supported when RNA synthesis was measured at a range of redox potentials. This gave a measured redox potential for the control of UTP incorporation into RNA of +270 mV and the slope of the curve indicated an n = 1 carrier. This value is close to the reported value of the Rieske iron-suphur protein. UTP incorporation was decreased by some 50% in the presence of low concentrations of okadaic acid (5 nM), an inhibitor of protein phosphatases PP1 and PP2A, and alpha-naphthyl acid phosphate, a broad-spectrum phosphatase inhibitor, indicating that the redox effect on RNA synthesis may be mediated via protein phosphorylation. We did not, however, detect an expected increase in RNA synthesis when protein kinase inhibitors were used, so the involvement of protein phosphorylation in the redox regulation of RNA synthesis is as yet uncertain.

Electron Transport↗
PubMed1976

The redox state and the concentration of ketone bodies in tissues of rats fed carbohydrate free diets.

The effect of carbohydrate free-low protein diets on the redox potential and ketone body concentrations in liver, muscle, and blood was investigated. Two carbohydrate free diets were fed: 1) A diet in which all the non-protein energy was provided by fatty acids (FA); 2) A similar diet in which the fatty acids were substituted by neutral fat (NF). A carbohydrate rich diet (HC) was fed for comparison. The redox potentials in cytoplasma and mitochondria were calculated from the relative concentrations of the [lactate]:[pyruvate] and [beta-hydroxy-butyrate]:[acetoacetate] couples respectively. In fed rats the cytoplasmic redox potential in liver was much higher in FA than in NF rats, but in fasted NF rats it increased markedly and equaled that of FA rats. In liver mitochondria the redox potential was lower in fed FA than in fed NF rats, while after a 24 hour fast it increased in FA rats and decreased in NF rats. Total ketone body concentrations were high in fed NF rats and increased further in fasted rats, however, in FA rats the high concentrations in the fed state decreased after the short fast. The changes of total ketone-bodies in blood and muscle followed those in liver in both fed and fasted states.

Acetoacetates↗
PubMed1997

Unusual lack of internal mobility and fast overall tumbling in oxidized flavodoxin from Anacystis nidulans.

Anacystis nidulans flavodoxin, an electron-transfer protein containing a flavin mononucleotide (FMN) molecule as its prosthetic group, has a redox potential for the oxidized/semiquinone equilibrium close to that of free flavin. Whereas the redox potential for the semiquinone/hydroquinone equilibrium is more negative. To gain an understanding of the contribution of mobility to redox potential modulation, we studied the backbone mobility of the oxidized A. nidulans flavodoxin at pH 6.6, 303 K by 15N NMR relaxation measurements. The spin-lattice relaxation rate constants (RN(Nz)=1/T1), spin-spin relaxation rate constants (RN(Nx,y)=1/T2) and 1H-15N nuclear Overhauser effects (NOE) were obtained for 143 of the 166 protonated backbone 15N nuclei and for the FMN N3 nucleus without ambiguity. The 15N T1, T2 and NOE data were analyzed by reduced spectral density mapping, and the so-called model-free approach. In contrast to most other proteins studied with 15N relaxation experiments, we found an almost complete absence of internal mobility. The overall correlation time of this 169-residue flavodoxin (>19 kDa) is significantly shorter (7.4 to 7.8 ns) than that of other proteins of this size, suggesting that the absence of internal mobility is correlated with faster overall rotational diffusion. The uniformity of the motional parameters along the backbone is in strong contrast to the crystallographic B-factors, which vary significantly along the sequence in this and other flavodoxins. The NMR relaxation parameters are primarily sensitive to rotational diffusive motions of the N-H bond vectors, while the crystallographic B-factors would be sensitive to translational internal motions as well. However, the large B-factors in this protein may originate from crystal packing and crystal lattice disorder. The relatively fast overall tumbling results in sharp NMR resonances. Hence, much larger proteins with such favorable dynamic behavior could be excellent candidates for studies by NMR.

Computer Simulation↗
PubMedDate not supplied

Time course of the redox state potential of the cerebral cortex, developing as a reaction to implanted platinum electrodes.

The time course of the redox-state potential of the brain (ROSP) of the brain was investigated in five series of chronic experiments in rabbits with different numbers of electrodes (8-12, 22-25, 50) implanted to the level of the dura mater, with 10-12 electrodes implanted to the level of the pia mater, and with four to eight pairs of electrodes implanted in the cortical layer to a distance of 1.5-2 mm. It was found that the ROSP undergoes a number of fluctuations in the negative and positive directions with a gradually decreasing amplitude in the course of 5-25 days following the operation, after which relatively stable negative values of the ROSP are established on the average in electrodes implanted to the level of the dura mater, and positive values in electrodes implanted to the level of the pia mater.

Animals↗
PubMed2001

Chromium diffusion and reduction in soil aggregates.

The distribution of metal contaminants such as chromium in soils can be strongly localized by transport limitations and redox gradients within soil aggregates. Measurements of Cr(VI) diffusion and reduction to Cr(III) were obtained in soil columns representing transects into soil aggregates in order to quantify influences of organic carbon (OC) and redox potentials on Cr transport distances and microbial community composition. Shifts in characteristic redox potentials, and the extent of Cr(VI) reduction to Cr(III) were related to OC availability. Depth profiles of Cr(VI, III) obtained with micro X-ray absorption near edge structure (micro-XANES) spectroscopy reflected interdependent effects of diffusion and spatially dependent redox potentials on reduction kinetics and microbial community composition. Shallow diffusion depths (2-10 mm) and very sharply terminated diffusion fronts in columns amended with OC (80 and 800 ppm) reflected rapid increases in Cr reduction kinetics over very short (mm) distances. These results suggest that Cr contamination in soils can be restricted to the outsides of soil aggregates due to localized transport and rapid reduction and that bulk sample characterization is inadequate for understanding the controlling biogeochemical processes.

Chromium↗
PubMed1980

Quantitative suspension test for the evaluation of disinfectants for swimming pool water: experiences with sodium hypochlorite and sodium dichloroisocyanurate.

To evaluate products intended for disinfection of water in swimming pools a quantitative suspension test was designed based on the principle of the Dutch standard suspension test (SST). As artifical swimming pool water a buffered bovine albumin solution (BBAS) was used. The microbicidal potency of BBAS chlorinated with sodium hypochlorite (NaOC1) for 5 min to free chlorine concentractions of 0.3, 0.5 and 1 mg/1 appeared to meet the tentative standard of 4 decimals reduction (D.R.) within 5 min against the bacterial test strains used, e.g. Staph, aureus, Str. faecalis, P. aeruginosa, E. coli and Prot. mirabilis. Usually an exposure time of 30 s was sufficient to obtain this reduction. The kill C. albicans to that extent approx. 1 mg/1 free chlorine was needed. The redox potential of BBAS chlorinated as described above amounted to approx. 600 mV or higher values. When BBAS was chlorinated for 5 min with sodium dichloroisocyanurate (NaDCC) addition of 8 mg/1 of this substance was required to obtain about the same microbicidal potency as that of BBAS chlorinated with NaOC1 to 0.3 mg/1 free chlorine. The redox potential in the former solution was found to be above 600 mV. The microbicidal potency of BBAS chlorinated for 5 minutes with 2 mg/1 NaDCC was virtually zero and with 4 mg/1 NaDCC suboptimal. These findings correlated well with the redox potentials of 262 mV and 432 mV, respectively, measured in the latter solutions. Addition of cyanuric acid to BBAS before chlorination resulted in lower killing rates, although the free chlorine concentration, determined with the FAS-DPD method, seemed to be increased. It is concluded that in swimming pool water chlorinated with chloroisocyanurates the redox potential might be a better indicator for the microbicidal potency than the free chlorine concentration determined with the FAS-DPD method.

Albumins↗
PubMed1986

Redox pathways in electron-transfer proteins: correlations between reactivities, solvent exposure, and unpaired-spin-density distributions.

The relative reactivities toward reduction by free flavin semiquinones of cytochromes (c-type cytochromes, cytochrome b5, c'-type cytochromes) iron-sulfur proteins (high-redox-potential ferredoxins, rubredoxins, low-redox-potential ferredoxins), and blue copper proteins (plastocyanin, azurins) are shown to correlate with calculations of the solvent exposure of the various prosthetic groups. In the case of the c-type cytochromes, one of the major centers of exposure is the sulfur atom of the thioether bridge that covalently links heme ring C to the protein. Charge-iterative extended Hückel calculations on a heme c model indicate that both porphyrin pi and Fe(III)d pi orbitals can delocalize onto the bridging sulfur atom. Unpaired spin densities are comparable to those obtained for individual aromatic porphyrin ring carbon atoms. Thus, the exposed sulfur of ring C may act to facilitate electron transfer.

Animals↗
PubMed2004

Biochemical regulation of mammalian AMP-activated protein kinase activity by NAD and NADH.

AMP-activated protein kinase (AMPK) serves as an energy-sensing protein kinase that is activated by a variety of metabolic stresses that lower cellular energy levels. When activated, AMPK modulates a network of metabolic pathways that result in net increased substrate oxidation, generation of reduced nucleotide cofactors, and production of ATP. AMPK is activated by a high AMP:ATP ratio and phosphorylation on threonine 172 by an upstream kinase. Recent studies suggest that mechanisms that do not involve changes in adenine nucleotide levels can activate AMPK. Another sensor of the metabolic state of the cell is the NAD/NADH redox potential. To test whether the redox state might have an effect on AMPK activity, we examined the effect of beta-NAD and NADH on this enzyme. The recombinant T172D-AMPK, which was mutated to mimic the phosphorylated state, was activated by beta-NAD in a dose-dependent manner, whereas NADH inhibited its activity. We explored the effect of NADH on AMPK by systematically varying the concentrations of ATP, NADH, peptide substrate, and AMP. Based on our findings and established activation of AMPK by AMP, we proposed a model for the regulation by NADH. Key features of this model are as follows. (a) NADH has an apparent competitive behavior with respect to ATP and uncompetitive behavior with respect to AMP resulting in improved binding constant in the presence of AMP, and (b) the binding of the peptide is not significantly altered by NADH. In the absence of AMP, the binding constant of NADH becomes higher than physiologically relevant. We conclude that AMPK senses both components of cellular energy status, redox potential, and phosphorylation potential.

AMP-Activated Protein Kinases↗
PubMed1997

Environmental effects on the growth and proteolysis of Treponema denticola ATCC 33520.

The effect of pH, redox potential, O2 and H2 on the growth and proteolytic activity of Treponema denticola ATCC 33520 was studied in a chemostat at different growth rates. The peptidase and protease activities were estimated using different amido-methyl coumarin derivatives and azocasein. The maximum growth rate of T. denticola ATCC 33520 was 0.14 h-1. Reduction of the growth rate of T. denticola by 50-60% gave: an increase in cell mass of 150-200%, a higher acetogenesis and a shift of the pH optimum. The protease and phenylalanine peptidase activities seemed to be of greater importance for the growth of T. denticola ATCC 33520 than the rather low arginine and proline peptidase activities. The redox potential (Eh) played a secondary role. At microaerophilic conditions with 1-5% O2, the cultures maintained a redox potential below -311 mV and an optimal acetogenesis. The presence of H2 induced a marked growth stimulation of T. denticola ATCC 33520. It is concluded that the cell mass and proteolytic activity of T. denticola ATCC 33520 are modulated by the growth rate and the pH and to a lesser extend by the redox potential and presence of O2. Stagnation of the exudate-flow influences these factors and will lead to an increase of the spirochetal population and proteolysis in the periodontal pocket.

Culture Media↗
PubMed2000

A thioredoxin from the hyperthermophilic archaeon Methanococcus jannaschii has a glutaredoxin-like fold but thioredoxin-like activities.

A thioredoxin homologue (Mj0307) from the hyperthermophilic archaeon Methanococcus jannaschii (MjTRX) was cloned, produced in E. coli, and compared to the thioredoxin from E. coli (ETRX). The secondary structure profile of MjTRX obtained by NMR spectroscopy shows that it has four beta-sheets and three alpha-helices arranged in betaalphabetaalphabetabetaalpha, similar to that of glutaredoxin. However, MjTRX supports the growth of T7 bacteriophage in E. coli and is weakly reduced by the thioredoxin reductase from E. coli, indicating that MjTRX is functionally closer to a thioredoxin than a glutaredoxin. MjTRX has higher specific insulin reductase activity than ETRX and retained its full activity over 4 days at 95 degrees C, whereas ETRX lost its activity in 150 min. The standard state redox potential of MjTRX is about -277 mV, which is the lowest value thus far known among redox potentials of the thioredoxin superfamily. This indicates that the lower redox potential is necessary in keeping catalytic disulfide bonds reduced in the cytoplasm and in coping with oxidative stress in an anaerobic hyperthermophile.

Amino Acid Sequence↗