scholarly journals Thiocyanate, a plausible physiological electron donor of gastric peroxidase

1995 ◽  
Vol 305 (1) ◽  
pp. 59-64 ◽  
Author(s):  
D Das ◽  
P K De ◽  
R K Banerjee
Keyword(s):  
Glutathione Reductase ◽  
Electron Donor ◽  
Order Rate Constant ◽  
Electron Donors ◽  
Compound I ◽  
Apparent Homogeneity ◽  
A Subunit ◽  
Nadph Oxidation ◽  
Compound Ii ◽  
Gastric Peroxidase

Gastric peroxidase (GPO) was purified to apparent homogeneity to characterize its major physiological electron donor. The enzyme (RZ = 0.7), with a subunit molecular mass of 50 kDa, is a glycoprotein, with a relative abundance of aspartic and glutamic acid over arginine and lysine. It has a Soret maximum at 412 nm, which is shifted to 426 nm by H2O2 due to formation of compound II. Although the physiological electron donors I-, Br- and SCN-, but not Cl-, are oxidized by GPO optimally at acid pH, only I- and SCN- are oxidized appreciably at physiological pH. Considering that the I- concentration in stomach is less than 1 microM, whereas the SCN- concentration is about 250 microM, SCN- may act as a major electron donor for GPO. Moreover, SCN- oxidation remains unaltered in the presence of physiological concentrations of other halides. The second-order rate constant for the reaction of GPO with H2O2 (k1) and compound I with SCN- (k2) at pH 7 was found to be 8 x 10(7) M-1.s-1 and 2 x 10(5) M-1.s-1 respectively. GPO has significant pseudocatalase activity also in the presence of I- or Br-, but it is blocked by SCN-. The SCN- oxidation product OSCN- may be reduced back to SCN- by cellular GSH, and GSSG may be reduced back to GSH by glutathione reductase and NADPH. In a system reconstituted with pure glutathione reductase, NADPH, GSH, SCN- and H2O2. GPO-catalysed SCN- oxidation could be coupled to NADPH oxidation. This system where GPO utilizes SCN- as the major physiological electron donor may operate efficiently to scavenge intracellular H2O2.

Reaction of human peroxidasin 1 compound I and compound II with one-electron donors

2020 ◽  
Vol 681 ◽  
pp. 108267 ◽  
Author(s):  
Benjamin Sevcnikar ◽  
Martina Paumann-Page ◽  
Stefan Hofbauer ◽  
Vera Pfanzagl ◽  
Paul G. Furtmüller ◽  
...  
Keyword(s):  
Electron Donors ◽  
Compound I ◽  
Compound Ii

Studies on Horseradish Peroxidase. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

1973 ◽  
Vol 51 (4) ◽  
pp. 582-587 ◽  
Author(s):  
M. L. Cotton ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Rate Constant ◽  
Active Sites ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Compound I ◽  
Order Rate ◽  
Compound Ii ◽  
Kinetics Of

In order to investigate the nature of compounds I and II of horseradish peroxidase, the kinetics were studied of ferrocyanide oxidation catalyzed by these compounds which were prepared from three different oxidizing agents. The pH dependence of the apparent second-order rate constant for ferrocyanide oxidation by compound I, prepared from ethyl hydroperoxide and m-chloroperbenzoic acid, was interpreted in terms of an ionization on the enzyme with a pKa = 5.3, identical to that reported previously for hydrogen peroxide. The second-order rate constant for the compound II-ferrocyanide reaction also showed the same pH dependence for the three oxidizing substrates. However, with more accurate results, the compound II-ferrocyanide reaction was reinterpreted in terms of a single ionization with pKa = 8.5. The same dependence of ferrocyanide oxidation on pH suggests structurally identical active sites for compounds I and II prepared from the three different oxidizing substrates.

Reactions of prostaglandin H synthase in the presence of the stabilizing agents diethyldithiocarbamate and glycerol

1990 ◽  
Vol 68 (6) ◽  
pp. 965-972 ◽  
Author(s):  
Yuchiong Hsuanyu ◽  
H. Brian Dunford
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Second Order ◽  
Prostaglandin H Synthase ◽  
Compound I ◽  
Stabilizing Agents ◽  
Order Rate ◽  
Ability To Act ◽  
Prostaglandin H ◽  
Compound Ii

Both cyclooxygenase and peroxidase reactions of prostaglandin H synthase were studied in the presence and absence of diethyldithiocarbamate and glycerol at 4 °C in phosphate buffer (pH 8.0). Diethyldithiocarbamate reacts with the high oxidation state intermediates of prostaglandin H synthase; it protects the enzyme from bleaching and loss of activity by its ability to act as a reducing agent. For the reaction of diethyldithiocarbamate with compound I, the second-order rate constant K2,app, was found to fall within the range of 5.8 × 106 ± 0.4 × 106 M−1∙s−1 < K2,app < 1.8 × 107 ± 0.1 × 107 M−1∙s−1. The reaction of diethyldithiocarbamate with compound II showed saturation behavior suggesting enzyme–substrate complex formation, with kcat = 22 ± 3 s−1, Km = 67 ± 10 μM, and the second-order rate constant k3,app = 2.0 × 105 ± 0.2 × 105 M−1∙s−1. In the presence of both diethyldithiocarbamate and 30% glycerol, the parameters for compound II are kcat = 8.8 ± 0.5 s−1, Km = 49 ± 7 μM, and k3,app = 1.03 × 105 ± 0.07 × 105 M−1∙s−1. The spontaneous decay rate constants of compounds I and II (in the absence of diethyldithiocarbamate) are 83 ± 5 and 0.52 ± 0.05 s−1, respectively, in the absence of glycerol; in the presence of 30% glycerol they are 78 ± 5 and 0.33 ± 0.02 s−1, respectively. Neither cyclooxygenase activity nor the rate constant for compound I formation using 5-phenyl-4-pentenyl-1-hydroperoxide is altered by the presence of diethyldithiocarbamate. It is suggested that kinetic studies on this enzyme can be performed in the presence of diethyldithiocarbamate, if one is cognizant of the rate of reaction of the stabilizing agent with compounds I and II and corrects for it if necessary.Key words: prostaglandin H synthase, diethyldithiocarbamate, cyclooxygenase, peroxidase, stabilizing agents.

Kinetics of oxidation of serotonin by myeloperoxidase compounds I and II

1999 ◽  
Vol 77 (5) ◽  
pp. 449-457 ◽  
Author(s):  
H Brian Dunford ◽  
Yuchiong Hsuanyu
Keyword(s):  
Rate Constant ◽  
Blood Platelets ◽  
Transient State ◽  
Order Rate Constant ◽  
Compound I ◽  
Kinetic Measurements ◽  
Order Of Magnitude ◽  
Electron Reduction ◽  
Ph Range ◽  
Compound Ii

The oxidation of serotonin (5-hydroxytryptamine) by the myeloperoxidase intermediates compounds I and II was investigated by using transient-state spectral and kinetic measurements at 25.0 ± 0.1°C. Rapid scan spectra demonstrated that both compound I and compound II oxidize serotonin via one-electron processes. Rate constants for these reactions were determined using both sequential-mixing and single-mixing stopped-flow techniques. The second order rate constant obtained for the one-electron reduction of compound I to compound II by serotonin is (1.7 ± 0.1) × 107 M-1·s-1, and that for compound II reduction to native enzyme is (1.4 ± 0.1) × 106 M-1·s-1 at pH 7.0. The maximum pH of the compound I reaction with serotonin occurs in the pH range 7.0-7.5. At neutral pH, the rate constant for myeloperoxidase compound I reacting with serotonin is an order of magnitude larger than for its reaction with chloride, (2.2 ± 0.2) × 106 M-1·s-1. A direct competition of serotonin with chloride for myeloperoxidase compound I oxidation was observed. Our results suggest that serotonin may have a role to protect lipoproteins from oxidation and to prevent enzymes from inactivation caused by the potent oxidants HOCl and active oxygen species.Key words: serotonin oxidation, myeloperoxidase, chloride, competition of serotonin, blood platelets, neutrophils.

scholarly journals Characterization of sheep lacrimal-gland peroxidase and its major physiological electron donor

1996 ◽  
Vol 314 (2) ◽  
pp. 413-419 ◽  
Author(s):  
Abhijit MAZUMDAR ◽  
Ratna CHATTERJEE ◽  
Subrata ADAK ◽  
Anil GHOSH ◽  
Chhabinath MONDAL ◽  
...  
Keyword(s):  
Molecular Mass ◽  
Electron Donor ◽  
Lacrimal Gland ◽  
Coupled System ◽  
Antigenic Determinants ◽  
Compound I ◽  
Native Molecular Mass ◽  
Apparent Homogeneity ◽  
Sigmoidal Curve

A soluble sheep lacrimal-gland peroxidase was purified to apparent homogeneity. It had a native molecular mass of 75 kDa with a subunit molecular mass of 82 kDa and an isoelectric point of 6.5. Western blotting showed that it shares some of the enzyme antigenic determinants in common with other soluble peroxidases. The enzyme exhibits a Soret peak at 410 nm which is shifted to 431 nm by 5 equiv. of H2O2 due to the formation of compound II. The latter is, however, unstable and gradually returns to the native state. The enzyme forms complexes with CN- and N3- and is reduced by dithionite showing a characteristic reduced peroxidase spectrum. Although the enzyme oxidizes I-, SCN- and Br- optimally at pH 5.5, 5.25 and 5.0 respectively, at physiological pH, it oxidizes I- and SCN- only. Since extracellular SCN- concentration is much higher than I-, SCN- may act as the major electron donor to the enzyme. The second-order rate constants for the reaction of the enzyme with H2O2 (k+1) and of compound I with SCN- (k+2) were 4×107 M-1·s-1 and 8.1×105 M-1·s-1 respectively. A plot of log Vmax. against pH yields a sigmoidal curve consistent with a single ionizable group on the enzyme with a pKa value of 5.75, controlling thiocyanate oxidation. In a coupled system with the peroxidase, H2O2, SCN-, GSH, NADPH and glutathione reductase, peroxidase-catalysed SCN- oxidation by H2O2 could be coupled to NADPH consumption. The system is proposed to operate in vivo for the efficient elimination of endogenous H2O2.

scholarly journals Influence of superoxide on myeloperoxidase kinetics measured with a hydrogen peroxide electrode

1989 ◽  
Vol 263 (3) ◽  
pp. 823-828 ◽  
Author(s):  
A J Kettle ◽  
C C Winterbourn
Keyword(s):  
Hypochlorous Acid ◽  
Initial Rate ◽  
Electron Donors ◽  
H2o2 Concentration ◽  
Compound I ◽  
Ph Optimum ◽  
Neutral Ph ◽  
High Concentrations ◽  
Compound Ii ◽  
Enzyme Functions

Stimulated neutrophils discharge large quantities of superoxide (O2.-), which dismutates to form H2O2. In combination with Cl-, H2O2 is converted into the potent oxidant hypochlorous acid (HOCl) by the haem enzyme myeloperoxidase. We have used an H2O2 electrode to monitor H2O2 uptake by myeloperoxidase, and have shown that in the presence of Cl- this accurately represents production of HOCl. Monochlorodimedon, which is routinely used to assay production of HOCl, inhibited H2O2 uptake by 95%. This result confirms that monochlorodimedon inhibits myeloperoxidase, and that the monochlorodimedon assay grossly underestimates the activity of myeloperoxidase. With 10 microM-H2O2 and 100 mM-Cl-, myeloperoxidase had a neutral pH optimum. Increasing the H2O2 concentration to 100 microM lowered the pH optimum to pH 6.5. Above the pH optimum there was a burst of H2O2 uptake that rapidly declined due to accumulation of Compound II. High concentrations of H2O2 inhibited myeloperoxidase and promoted the formation of Compound II. These effects of H2O2 were decreased at higher concentrations of Cl-. We propose that H2O2 competes with Cl- for Compound I and reduces it to Compound II, thereby inhibiting myeloperoxidase. Above pH 6.5, O2.- generated by xanthine oxidase and acetaldehyde prevented H2O2 from inhibiting myeloperoxidase, increasing the initial rate of H2O2 uptake. O2.- allowed myeloperoxidase to function optimally with 100 microM-H2O2 at pH 7.0. This occurred because, as previously demonstrated, O2.- prevents Compound II from accumulating by reducing it to ferric myeloperoxidase. In contrast, at pH 6.0, where Compound II did not accumulate, O2.- retarded the uptake of H2O2. We propose that by generating O2.- neutrophils prevent H2O2 and other one-electron donors from inhibiting myeloperoxidase, and ensure that this enzyme functions optimally at neutral pH.

scholarly journals Interplay between Oxo and Fluoro in Vanadium Oxyfluorides for Centrosymmetric and Non-Centrosymmetric Structure Formation

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 603
Author(s):  
Prashanth Sandineni ◽  
Hooman Yaghoobnejad Asl ◽  
Weiguo Zhang ◽  
P. Shiv Halasyamani ◽  
Kartik Ghosh ◽  
...  
Keyword(s):  
Second Harmonic ◽  
Metastable Phase ◽  
Compound I ◽  
Hydrothermal Route ◽  
Prolonged Heating ◽  
Space Group ◽  
Lithium Vanadium Oxide ◽  
Compound Ii ◽  
Unambiguous Assignment ◽  
Centrosymmetric Structure

Herein, we report the syntheses of two lithium-vanadium oxide-fluoride compounds crystallized from the same reaction mixture through a time variation experiment. A low temperature hydrothermal route employing a viscous paste of V2O5, oxalic acid, LiF, and HF allowed the crystallization of one metastable phase initially, Li2VO0.55(H2O)0.45F5⋅2H2O (I), which on prolonged heating transforms to a chemically similar yet structurally different phase, Li3VOF5 (II). Compound I crystallizes in centrosymmetric space group, I2/a with a = 6.052(3), b = 7.928(4), c = 12.461(6) Å, and β = 103.99(2)°, while compound II crystallizes in a non-centrosymmetric (NCS) space group, Pna21 with a = 5.1173(2), b = 8.612(3), c = 9.346(3) Å. Synthesis of NCS crystals are highly sought after in solid-state chemistry for their second-harmonic-generation (SHG) response and compound II exhibits SHG activity albeit non-phase-matchable. In this article, we also describe their magnetic properties which helped in unambiguous assignment of mixed valency of V (+4/+5) for Li2VO0.55(H2O)0.45F5⋅2H2O (I) and +4 valency of V for Li3VOF5 (II).

scholarly journals A Microcosm Treatability Study for Evaluating Wood Mulch-Based Amendments as Electron Donors for Trichloroethene (TCE) Reductive Dechlorination

Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1949
Author(s):  
Edoardo Masut ◽  
Alessandro Battaglia ◽  
Luca Ferioli ◽  
Anna Legnani ◽  
Carolina Cruz Viggi ◽  
...  
Keyword(s):  
Electron Donor ◽  
Environmental Sustainability ◽  
Reductive Dechlorination ◽  
Environmental Remediation ◽  
Low Cost ◽  
Chlorinated Solvents ◽  
Electron Donors ◽  
Chlorinated Ethenes ◽  
Dehalococcoides Mccartyi ◽  
Wood Mulch

In this study, wood mulch-based amendments were tested in a bench-scale microcosm experiment in order to assess the treatability of saturated soils and groundwater from an industrial site contaminated by chlorinated ethenes. Wood mulch was tested alone as the only electron donor in order to assess its potential for stimulating the biological reductive dechlorination. It was also tested in combination with millimetric iron filings in order to assess the ability of the additive to accelerate/improve the bioremediation process. The efficacy of the selected amendments was compared with that of unamended control microcosms. The results demonstrated that wood mulch is an effective natural and low-cost electron donor to stimulate the complete reductive dechlorination of chlorinated solvents to ethene. Being a side-product of the wood industry, mulch can be used in environmental remediation, an approach which perfectly fits the principles of circular economy and addresses the compelling needs of a sustainable and low environmental impact remediation. The efficacy of mulch was further improved by the co-presence of iron filings, which accelerated the conversion of vinyl chloride into the ethene by increasing the H2 availability rather than by catalyzing the direct abiotic dechlorination of contaminants. Chemical analyses were corroborated by biomolecular assays, which confirmed the stimulatory effect of the selected amendments on the abundance of Dehalococcoides mccartyi and related reductive dehalogenase genes. Overall, this paper further highlights the application potential and environmental sustainability of wood mulch-based amendments as low-cost electron donors for the biological treatment of chlorinated ethenes.

scholarly journals Ionization characteristics of the Cys-25/His-159 interactive system and of the modulatory group of papain: resolution of ambiguity by electronic perturbation of the quasi-2-mercaptopyridine leaving group in a new pyrimidyl disulphide reactivity probe

1993 ◽  
Vol 290 (1) ◽  
pp. 289-296 ◽  
Author(s):  
G W Mellor ◽  
E W Thomas ◽  
C M Topham ◽  
K Brocklehurst
Keyword(s):  
Ph Dependence ◽  
Order Rate Constant ◽  
Ion Pair ◽  
Catalytic Site ◽  
Alkaline Media ◽  
Interactive System ◽  
Data Set ◽  
Pka Value ◽  
Compound Ii ◽  
Pair State

1. A new thiol-specific reactivity probe 4,4′-dipyrimidyl disulphide [compound (VII), m.p. 110 degrees C, pKa of its monohydronated form 0.91] was synthesized and used to resolve the ambiguity of interpretation of the behaviour of papain (EC 3.4.22.2) in alkaline media known to depend to varying extents on two ionizations with pKa values approx. 8.0-8.5 and > or = 9.5 respectively. 2. A new extensive pH-second-order rate constant (k) data set for the reaction of papain with 2-(acetamido)-ethyl 2′-pyridyl disulphide (IV) demonstrated the existence of a striking rate maximum at pH approx. 4, the independence of k around pH 8 and the increase in k with increase in pH across a pKa value of 10.0, behaviour similar to that of other 2-pyridyl disulphides (R-S-S-2-Py) that lack key substrate-like binding sites in R. 3. Although the simplest interpretation of the pKa value of 10.0 assigns it to the formation of (Cys-25)-S-/(His-159)-Im from the ion-pair state of the papain catalytic site, another interpretation may be conceived in which this pKa value is assigned to another group remote from the catalytic site, the state of ionization of which modulates catalytic-site behaviour. This alternative assignment is shown to require compensating effects in the pH region around 8 such that the formation of (Cys-25)-S-/(His-159)-Im across pKa 8.0-8.5 is without net kinetic effect in the reactions of simple 2-pyridyl disulphides such as compound (IV) and 2,2′-dipyridyl disulphide (II). 4. The lower basicity of compound (VII) relative to that of compound (II) (pKa 2.45) was predicted to diminish or abolish the compensation postulated as a possibility in reactions of 2-pyridyl disulphides because of the decreased effectiveness of reaction via a (His-159)-Im+H-assisted transition state. The characteristics of the pH-dependence of the reaction of papain with compound (VII) which are quite different from those for its reaction with compound (II) support both this prediction and the alternative assignment with a value of 8.3 for the pKa of the formation of (Cys-25)-S-/(His-159)-Im. 5. Evidence that the behaviour of papain towards both substrates and some substrate-derived time-dependent inhibitors is determined not only by the loss of the (Cys-25)-S-/(His-159)-Im+H ion-pair state by dehydronation with pKa 8.3 but also by another ionization of pKa approx. 10.0 is briefly discussed.

scholarly journals Crystal structures of {[Cu(Lpn)2][Fe(CN)5(NO)]·H2O}nand {[Cu(Lpn)2]3[Cr(CN)6]2·5H2O}n[where Lpn = (R)-propane-1,2-diamine]: two heterometallic chiral cyanide-bridged coordination polymers

2015 ◽  
Vol 71 (4) ◽  
pp. 392-397
Author(s):  
Olha Sereda ◽  
Helen Stoeckli-Evans
Keyword(s):  
Hydrogen Bonds ◽  
Coordination Polymers ◽  
Three Dimensional ◽  
Water Molecules ◽  
Two Dimensional ◽  
Asymmetric Unit ◽  
Compound I ◽  
Distorted Octahedral ◽  
Coordination Spheres ◽  
Compound Ii

The title compounds,catena-poly[[[bis[(R)-propane-1,2-diamine-κ2N,N′]copper(II)]-μ-cyanido-κ2N:C-[tris(cyanido-κC)(nitroso-κN)iron(III)]-μ-cyanido-κ2C:N] monohydrate], {[Cu(Lpn)2][Fe(CN)5(NO)]·H2O}n, (I), and poly[[hexa-μ-cyanido-κ12C:N-hexacyanido-κ6C-hexakis[(R)-propane-1,2-diamine-κ2N,N′]dichromium(III)tricopper(II)] pentahydrate], {[Cu(Lpn)2]3[Cr(CN)6]2·5H2O}n, (II) [where Lpn = (R)-propane-1,2-diamine, C3H10N2], are new chiral cyanide-bridged bimetallic coordination polymers. The asymmetric unit of compound (I) is composed of two independent cation–anion units of {[Cu(Lpn)2][Fe(CN)5)(NO)]} and two water molecules. The FeIIIatoms have distorted octahedral geometries, while the CuIIatoms can be considered to be pentacoordinate. In the crystal, however, the units align to form zigzag cyanide-bridged chains propagating along [101]. Hence, the CuIIatoms have distorted octahedral coordination spheres with extremely long semicoordination Cu—N(cyanido) bridging bonds. The chains are linked by O—H...N and N—H...N hydrogen bonds, forming two-dimensional networks parallel to (010), and the networks are linkedviaN—H...O and N—H...N hydrogen bonds, forming a three-dimensional framework. Compound (II) is a two-dimensional cyanide-bridged coordination polymer. The asymmetric unit is composed of two chiral {[Cu(Lpn)2][Cr(CN)6]}−anions bridged by a chiral [Cu(Lpn)2]2+cation and five water molecules of crystallization. Both the CrIIIatoms and the central CuIIatom have distorted octahedral geometries. The coordination spheres of the outer CuIIatoms of the asymmetric unit can be considered to be pentacoordinate. In the crystal, these units are bridged by long semicoordination Cu—N(cyanide) bridging bonds forming a two-dimensional network, hence these CuIIatoms now have distorted octahedral geometries. The networks, which lie parallel to (10-1), are linkedviaO—H...O, O—H...N, N—H...O and N—H...N hydrogen bonds involving all five non-coordinating water molecules, the cyanide N atoms and the NH2groups of the Lpn ligands, forming a three-dimensional framework.

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