Kinetic Studies on the Oxidation of Thiols by Coenzyme PQQ

Itoh, Shinobu; Kato, Nobuyuki; Mure, Minae; Ohshiro, Yoshiki

doi:10.1246/bcsj.60.420

Cited by 31 publications

(19 citation statements)

References 8 publications

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“…The scheme of the reduction of PQQ by PhSH was discussed by Itoh et al As they reported, one of the possible mechanisms is that involving C-5 attack of the thiolate ion followed by breakdown to reduced PQQ and the corresponding disulfide (see the scheme in ref 32). concentration of GSH of 9.60 × 10 -3 M).…”

Section: Resultsmentioning

confidence: 99%

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH₂, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Ouchi

Nakano

Nagaoka

et al. 2008

J. Agric. Food Chem.

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Kinetic study of the aroxyl radical-scavenging action of pyrroloquinolinequinol [PQQH(2), a reduced form of pyrroloquinolinequinone (PQQ)] and water-soluble antioxidants (vitamin C, cysteine, glutathione, and uric acid) has been performed. The second-order rate constants (k(s)) for the reaction of aroxyl radical with PQQH(2) and water-soluble antioxidants were measured in Triton X-100 micellar solution (5.0 wt %) (pH 7.4), using stopped-flow and UV-visible spectrophotometers. The k(s) values decreased in the order PQQH(2) > vitamin C >> cysteine > uric acid > glutathione. The aroxyl radical-scavenging activity of PQQH(2) was 7.4 times higher than that of vitamin C, which is well-known as the most active water-soluble antioxidant. Furthermore, PQQNa(2) (disodium salt of PQQ) was easily reduced to PQQH(2) by reaction of PQQNa(2) with glutathione and cysteine in buffer solution (pH 7.4) under nitrogen atmosphere. The result suggests that PQQ exists as a reduced form throughout the cell and plays a role as antioxidant.

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Section: Resultsmentioning

confidence: 99%

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH₂, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Ouchi

Nakano

Nagaoka

et al. 2008

J. Agric. Food Chem.

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“…Free PQQ has been shown to catalyze non-enzymatic reactions, including the oxidation of thiols to disulfide [24,25]. Taking advantage of the latter together with its redox property, PQQ has been applied for electrochemical detection of thiols [26,27].…”

Section: Introductionmentioning

confidence: 99%

Ormosil Encapsulated Pyrroloquinoline Quinone‐Modified Electrochemical Sensor for Thiols

et al. 2004

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An organically modified sol-gel glass (ORMOSIL) encapsulating pyrroloquinoline quinone (PQQ)-modified electrode for the rapid, sensitive and simple determination of thiol-containing compounds such as cysteine and glutathione is reported. The effect of applied potential, nature of thiol compound and pH on the response of the sensor was examined and optimum conditions were determined. The electrochemical responses and detection limits were found to be sensitive to the nature of thiols and pH. The electrochemical responses for cysteine and glutathione at an applied potential of À 0.2 V (vs. Ag/AgCl) were found to be linear with detection limits of 18 nM for cysteine and 36 nM for glutathione at pH 3.5, whereas the detection limits at pH 8.5 were 0.5 mM for cysteine and 1 mM for glutathione. The electrode retained 95% of the original response for 7 days when stored at 4 8C. The ORMOSILencapsulated PQQ was also characterized by spectrophotometry. The absorbance measurement using 5,5'-dithiobis-(2-nitrobenzoic acid) at 412 nm justify the PQQ-mediated oxidation of glutathione whereas fluorescence measurements (excitation wavelength ¼ 380 nm; emission wavelength ¼ 480 nm) justify the successful encapsulation of PQQ in ORMOSIL matrix.

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“…In both cases the o-quinone moiety serves as an efficient electron shuttle without deactivation of the electrocatalyst. This unique combination of properties is attributed to the substituted o-quinone ring found in PQQ and TTQ that impedes 1,4-addition of nucleophiles.Interestingly, PQQ catalyzes non-enzymatic reactions such as the oxidation of thiols to disulfides [11,12], which we have utilized to develop sensitive and selective thiol detection strategies with PQQ entrapped in a polypyrrole conducting polymer membrane [7][8][9][10].As part of an effort to harness the electrocatalytic properties of the natural o-quinone cofactors, we have initiated research to synthesize o-quinone analogues with exceptional redox cycling capabilities similar to PQQ [13]. One challenge with this approach is maintaining electrocatalyst levels in the sensing membrane for extended time periods.…”

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confidence: 99%

In Situ Self Assembly of Thiolated ortho‐Quinone Capped Electrocatalysts for Bioanalytical Applications

et al. 2011

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Thiolated o-quinone-capped electrocatalysts modeled on the naturally occurring o-quinone cofactor pyrroloquinoline quinone (PQQ) were designed and synthesized for the development of biosensor devices. The o-quinonecapped electrocatalysts self assembled on gold electrodes through a thiolated phenyleneethynylene linkage to form a monolayer less than 2 nm in thickness. Cyclic voltammetric measurements demonstrated reversible electrochemical properties between the quinone and hydroquinone forms of the head group. In an amperometric sensing mode, the modified electrodes reproducibly detected ethanethiol at micromolar levels demonstrating their robust electrocatalytic activity toward thiols. Their redox cycling and electrocatalytic properties show promise for detection of biologically important thiols and other nucleophiles. Redox-cycling quinones play important roles in biological signaling, metabolic pathways, gene expression, and disease prevention [1]. Their widespread incorporation in biological processes results from the efficiency of the quinone electron-transfer and their reactivity to nucleophiles. The redox active o-quinone moiety exhibits an efficient, pH-dependent reversible electron transfer between its oxidized and reduced forms, which makes o-quinones attractive electrocatalysts for molecular devices and sensors [2]. However, one drawback is the binding of reactive nucleophiles by Michael type addition. Although this property can be exploited to develop biosensing devices to detect biomarkers and infectious agents through binding of DNA, proteins and other biomolecules containing nucleophilic groups [3][4][5], it compromises their integrity as redox-cycling electrocatalysts for biosensor applications.Two recent examples of sensors based on naturally occurring o-quinone redox cofactors utilize tryptophan tryptophylquinone (TTQ) [6] and pyrroloquinoline quinone (PQQ) [7][8][9][10]. In both cases the o-quinone moiety serves as an efficient electron shuttle without deactivation of the electrocatalyst. This unique combination of properties is attributed to the substituted o-quinone ring found in PQQ and TTQ that impedes 1,4-addition of nucleophiles.Interestingly, PQQ catalyzes non-enzymatic reactions such as the oxidation of thiols to disulfides [11,12], which we have utilized to develop sensitive and selective thiol detection strategies with PQQ entrapped in a polypyrrole conducting polymer membrane [7][8][9][10].As part of an effort to harness the electrocatalytic properties of the natural o-quinone cofactors, we have initiated research to synthesize o-quinone analogues with exceptional redox cycling capabilities similar to PQQ [13]. One challenge with this approach is maintaining electrocatalyst levels in the sensing membrane for extended time periods. In order to improve sensor stability and also enhance the versatility for thiol detection, we have designed and synthesized second generation o-quinone electrocatalysts, where the o-quinone is anchored to the electrode via a thiol-terminated electric...

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Kinetic Studies on the Oxidation of Thiols by Coenzyme PQQ

Cited by 31 publications

References 8 publications

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH₂, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH₂, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Ormosil Encapsulated Pyrroloquinoline Quinone‐Modified Electrochemical Sensor for Thiols

In Situ Self Assembly of Thiolated ortho‐Quinone Capped Electrocatalysts for Bioanalytical Applications

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Kinetic Studies on the Oxidation of Thiols by Coenzyme PQQ

Cited by 31 publications

References 8 publications

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH2, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH2, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Ormosil Encapsulated Pyrroloquinoline Quinone‐Modified Electrochemical Sensor for Thiols

In Situ Self Assembly of Thiolated ortho‐Quinone Capped Electrocatalysts for Bioanalytical Applications

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Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH₂, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution

Kinetic Study of the Antioxidant Activity of Pyrroloquinolinequinol (PQQH₂, a Reduced Form of Pyrroloquinolinequinone) in Micellar Solution