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Results for “PQQ Cofactor”

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PubMed1992

Mediated amperometric determination of xylose and glucose with an immobilized aldose dehydrogenase electrode.

An enzyme electrode was constructed for amperometric determination of xylose and glucose. The electrode is based on the PQQ-dependent membrane-bound aldose dehydrogenase (ALDH) from Gluconobacter oxydans. ALDH was covalently immobilized on a graphite electrode. Immobilized dimethylferrocene, soluble ferrocene carboxylic acid and phenazine methosulphate were used as electron transfer mediators. When xylose was measured electrochemically using an electrode modified with ALDH and dimethylferrocene, the linear measurement range extended to 100 mM. For glucose measurement the linear measurement range was about one-tenth of that for xylose. The electrode showed fairly good stability; 50% of the original electrode response was still obtained after 5 days of intermittent use. The effect of possible leakage of adsorbed mediator was determined by measuring the response of an electrode with soluble mediator as a function of time. The reproducibility of the electrode was good, the standard deviation of the electrode response in ten measurements with the same electrode being only 2.7%.

Biosensing Techniques↗
PubMed1989

PQQ, the elusive coenzyme.

The recently discovered redox coenzyme, PQQ (methoxatin), is widely distributed. Quantitation of protein-bound PQQ has been difficult, but unique redox cycling reactions, which reflect its striking biological properties, reveal trace amounts. PQQ is a potential target for drugs.

Animals↗
PubMed1990

PQQ in plants.

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Amine Oxidase (Copper-Containing)↗
PubMed2004

Hydrogen tunneling in quinoproteins.

It is now widely accepted that substrate C-H bond breakage by quinoprotein enzymes occurs by quantum mechanical tunneling. This paradigm shift in the conceptual framework for these reactions away from semi-classical transition state theory (i.e., including zero-point energy but with no tunneling correction) has been driven over recent years by experimental studies of the temperature dependence of kinetic isotope effects for these reactions in the TTQ-dependent enzymes methylamine dehydrogenase and aromatic amine dehydrogenase, which produced observations also inconsistent with the simple Bell correction model of tunneling. However, these data-specifically, the strong temperature dependence of reaction rates and the variable temperature dependence of kinetic isotope effects-are consistent with other tunneling models (denoted full tunneling models) in which protein and/or substrate fluctuations generate a configuration compatible with tunneling. These models accommodate substrate/protein (environment) fluctuations required to attain a configuration with degenerate quantum states and, when necessary, motion required to increase the probability of tunneling in these states. Furthermore, tunneling mechanisms in quinoproteins are supported by computational studies employing variational transition state theory with multidimensional tunneling corrections; these studies are also discussed in this review. Potential pitfalls in analyzing the temperature dependence of kinetic isotope effects as probes of tunneling are also discussed with reference to PQQ-dependent methanol dehydrogenase.

Dihydroxyphenylalanine↗
PubMed2004

Quinohemoprotein alcohol dehydrogenases: structure, function, and physiology.

Quino(hemo)protein alcohol dehydrogenases (ADH) that have pyrroloquinoline quinone (PQQ) as the prosthetic group are classified into 3 groups, types I, II, and III. Type I ADH is a simple quinoprotein having PQQ as the only prosthetic group, while type II and type III ADHs are quinohemoprotein having heme c as well as PQQ in the catalytic polypeptide. Type II ADH is a soluble periplasmic enzyme and is widely distributed in Proteobacteria such as Pseudomonas, Ralstonia, Comamonas, etc. In contrast, type III ADH is a membrane-bound enzyme working on the periplasmic surface solely in acetic acid bacteria. It consists of three subunits that comprise a quinohemoprotein catalytic subunit, a triheme cytochrome c subunit, and a third subunit of unknown function. The catalytic subunits of all the quino(hemo)protein ADHs have a common structural motif, a quinoprotein-specific superbarrel domain, where PQQ is deeply embedded in the center. In addition, in the type II and type III ADHs this subunit contains a unique heme c domain. Various type II ADHs each have a unique substrate specificity, accepting a wide variety of alcohols, as is discussed on the basis of recent X-ray crystallographic analyses. Electron transfer within both type II and III ADHs is discussed in terms of the intramolecular reaction from PQQ to heme c and also from heme to heme, and in terms of the intermolecular reaction with azurin and ubiquinone, respectively. Unique physiological functions of both types of quinohemoprotein ADHs are also discussed.

Alcohol Oxidoreductases↗
PubMed2003

Pyrroloquinoline-quinone synthesized in Escherichia coli by pyrroloquinoline-quinone synthase of Deinococcus radiodurans plays a role beyond mineral phosphate solubilization.

Deinococcus radiodurans, an extremely radioresistant bacterium, synthesizes coenzyme pyrroloquinoline-quinone (PQQ) but exhibits a negative phenotype for mineral phosphate solubilization. Gene for the putative PQQ synthesizing protein was PCR amplified and cloned from Deinococcus, sequenced, and expressed in Escherichia coli, under an inducible E. coli promoter. The transgenic E. coli expressed PQQ synthase protein of 42kDa and complemented the mineral phosphate solubilization phenotype of E. coli, suggesting the synthesis of an active protein. The cells expressing high levels of this protein showed increased protection against photodynamically produced reactive oxygen species. The effect could be attributed to the upregulation of antioxidant enzymes such as catalase and superoxide dismutase by PQQ in transgenic E. coli through an unknown mechanism. The study elucidates a hitherto unknown possible function of PQQ in bacteria.

Antioxidants↗
PubMed2007

Factors required for the catalytic reaction of PqqC/D which produces pyrroloquinoline quinone.

PqqC/D converts the biosynthetic intermediate purified from a pqqC mutant to pyrroloquinoline quinone (PQQ), and both NAD(P)H and cytosolic fraction, named as activating factor (ActF), are required to show its higher production. Dithiothreitol alone, as well as ActF plus NAD(P)H, enhanced the PQQ production by PqqC/D. Thioredoxin-thioredoxin reductase system with NADPH showed similar effect. PqqC/D made a tight complex with PQQ, however, in the presence of dithiothreitol, PQQ was dissociated from the protein. ActF showed NADPH oxidase activity which was enhanced by the addition of PQQ. These data suggest that PqqC/D produces the reduced PQQ from the intermediate in vivo, but in vitro, it is further oxidized by molecular oxygen and then the oxidized PQQ is trapped in PqqC/D to show product inhibition.

Bacterial Proteins↗
PubMed2005

Scanning electrochemical microscopy for detection of biosensor and biochip surfaces with immobilized pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase as enzyme label.

Scanning electrochemical microscopy (SECM) was applied to study quinoprotein-based biosensor or biochip. A typical quinoprotein, pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH), was taken as example. Feedback mode and generation collection (GC) mode in SECM have been explored in imaging the catalytic activity of GDH on microscopic magnetic bead domains. Biotinylated GDH was immobilized by using streptavidin-coated paramagnetic microbeads, which were deposited as microspot on a hydrophobic surface. Ferrocenemethanol and ferricyanide were used as electron mediators for feedback and GC detection, respectively. Enzymatic catalysis was further studied quantitatively using the theory developed for SECM.

Biosensing Techniques↗
PubMed2004

Wiring of PQQ-dehydrogenases.

The performance of pyrroloquinoline quinone (PQQ) dependent alcohol dehydrogenase (ADH) and two types of PQQ-glucose dehydrogenases in solution and when immobilized on the carbon paste electrodes modified with ferrocene derivatives is investigated. The immobilization of ADH consisting of PQQ and four hemes improves its stability up to 10 times. Both PQQ and heme moieties are involved in the electron transport from substrate to electrode. The ferrocene derivatives improve the electron transport 10-fold. Membrane-bound alcohol dehydrogenase from Gluconobacter sp. 33, intracellular soluble glucose dehydrogenase from Acinetobacter calcoaceticus L.M.D. 79.41 (s-GDH), and the membrane-bound enzyme (m-GDH) from Erwinia sp. 34-1 were purified and investigated. Soluble and membrane-bound PQQ-glucose dehydrogenases display different behavior during the immobilization on the modified carbon electrodes. The immobilization of s-GDH leads to a decrease in both stability and substrate specificity of the enzyme. This suggests that PQQ dissociates from the enzyme active center and operates as a free-diffusing mediator. The rate-limiting step of the process is likely the loading of PQQ onto the apo-enzyme. The immobilization of m-GDH leads to its substantial stabilization and improves the substrate specificity. The nature of m-GDH binding to the electrode surface is presumably similar to the binding to the cell membrane through its anchor-subunit. The enzyme operates as an enzyme and mediator complex.

Adsorption↗
PubMed2004

Pyrroloquinoline-quinone: a reactive oxygen species scavenger in bacteria.

Transgenic Escherichia coli expressing pyrroloquinoline-quinone (PQQ) synthase gene from Deinococcus radiodurans showed superior survival during Rose Bengal induced oxidative stress. Such cells showed significantly low levels of protein carbonylation as compared to non-transgenic control. In vitro, PQQ reacted with reactive oxygen species with rate constants comparable to other well known antioxidants, producing non-reactive molecular products. PQQ also protected plasmid DNA and proteins from the oxidative damage caused by gamma-irradiation in solution. The data suggest that radioprotective/oxidative stress protective ability of PQQ in bacteria may be consequent to scavenging of reactive oxygen species per se and induction of other free radical scavenging mechanism.

Animals↗
PubMed2004

Quinate oxidation in Gluconobacter oxydans IFO3244: purification and characterization of quinoprotein quinate dehydrogenase.

Quinoprotein quinate dehydrogenase (QDH) is a membrane-bound enzyme containing pyrroloquinoline quinone (PQQ) as the prosthetic group. QDH in Gluconobacter oxydans IFO3244 was found to be inducible by quinate and it is not constitutively expressed in the absence of quinate. The purification of holo-form of QDH to nearly homogeneity was achieved. The purified QDH appears to have two subunits of approximately 65 and 21 kDa, which could be the result of proteolysis of single polypeptide. Kinetic analysis indicated that the purified enzyme is much more specific to quinate than QDH from Acinetobacter calcoaceticus. The efficiency of the artificial electron acceptor was also determined.

Alcohol Oxidoreductases↗
PubMed2002

PqqC/D, which converts a biosynthetic intermediate to pyrroloquinoline quinone.

PqqC/D was purified from Escherichia coli transformant. The purified enzyme converted an intermediate that accumulated in a pqqC mutant of Methylobacterium extorquens AM1 to PQQ. The reaction did not show any dependence of NAD(P)H that was observed in the crude extract before purification. PqqC/D reacted with the intermediate stoichiometrically, but not catalytically. When partially purified proteins from the crude extract of E. coli were added to the reaction mixture, the rate of PQQ production increased dependent on the amount of NADPH added and the total amount of PQQ produced increased.

Bacterial Proteins↗
PubMed1986

The methoxatin semiquinone: a pulse radiolysis study.

Methoxatin is a novel o-quinone found in bacterial dehydrogenases and mammalian plasma amine oxidase. This is the first report of the redox potential and spectrum of the 1-electron reduced methoxatin semiquinone obtained by the method of pulse radiolysis in aqueous solution.

Kinetics↗
PubMed1986

The 9-carboxyl group of pyrroloquinoline quinone, a novel prosthetic group, is essential in the formation of holoenzyme of D-glucose dehydrogenase.

Availability of different analogues of pyrroloquinoline quinone as the prosthetic group for apo-D-glucose dehydrogenase was examined. The 9-carboxyl group of pyrroloquinoline quinone was shown to be essential for the reconstitution of the enzyme activity. Although the carboxyl group may not be involved in catalytic function, it is quite probable to contribute the binding of the prosthetic group to apoenzyme.

Carbohydrate Dehydrogenases↗