Enzyme pyrroloquinoline quinone

Shimao M, Ninomiya K, Kuno O, Kato N, Sakazawa C (1986), Existence of a novel enzyme, pyrroloquinoline quinone-dependent polyvinyl alcohol dehydrogenase, in a bacterial symbiont. Pseudomonas sp. strain VM15C , Appl Environ Microbiol, 51, 268-275. 

Fructose dehydrogenase (FDH) having pyrroloquinoline quinone (PQQ) as a prosthetic group is an redox enzyme to catalyze the oxidation of fructose. A... 

Examples of surface-immobilized mediators are electropolymerized azines for electro-oxidation of The extreme form of this approach is formation of biocatalytic monolayer, comprising a surface-bound mediator species that is itself bound to a single enzyme molecule. Katz et al. report a complete cell based on novel architecture at both electrodes (Figure 7). On the anode side, the FAD center of glucose oxidase is removed from the enzyme shell and covalently attached to a pyrroloquinoline quinone (PQQ) mediator species previously immobilized on a gold surface. The GOx apoenzyme (enzyme with active center removed) is reintroduced in solution and selectively binds to FAD, resulting in a PQQ-... 

Pyrroloquinoline quinone (PQQ) (or methoxatin) 6 is a coenzyme, responsible for the oxidation of methanol [7]. It has been found that cyclopropanol 4 inactivates the enzyme from M. methanica [8], the dimeric methanol dehydrogenase and the monomeric enzyme from a Pseudomonas PQQ-dependent methanol dehydrogenase [9] by forming adducts such as 7, through a one-electron oxidation process and the ready ring opening of a cyclopropyloxonium radical, Eq. (3) [8,9]. 

An additional condition may be imposed, even when a cofactor-independent enzyme is used, if a mediator molecule is involved in the electron transfer process, as is often the case with oxidases. Laccases, for example, may employ small-molecule diffusible mediator compounds in their redox cycle to shuttle electrons between the redox center of the enzyme and the substrate or electrode (Scheme 3.1) [1, 2]. Similarly, certain dehydrogenases utiHze pyrroloquinoline quinone. In biocatalytic systems, mediators based on metal complexes are often used. 

ZnS colloids were also used by Kuwabata et al. to photoreduce C02 to formate [130]. In this system, the ZnS colloids also reduced pyrroloquinoline quinone which served as an electron mediator to the enzyme, methanol dehydrogenase, which could then reduce formate to methanol. In C02-saturated aqueous solution at pH 7 and under far-UV (280nm) illumination, quantum efficiencies of 7% and 6% were achieved for formate and methanol, respectively. 

An alternative biosensor system has been developed by Hart et al. [44] which involves the use of the NAD+-dependent GDH enzyme. The first step of the reaction scheme involves the enzymatic reduction of NAD+ to NADH, which is bought about by the action of GDH on glucose. The analytical signal arises from the electrocatalytic oxidation of NADH back to NAD+ in the presence of the electrocatalyst Meldola s Blue (MB), at a potential of only 0Y. Biosensors utilising this mediator have been reviewed elsewhere [1,17]. Razumiene et al. [45] employed a similar system using both GDH and alcohol dehydrogenase with the cofactor pyrroloquinoline quinone (PQQ), the oxidation of which was mediated by a ferrocene derivative. 

The P. chlororaphis B23 NHase is the ferric enzyme [50], which has been characterized in detail [51,52]. (i) The NHase is the first known nonheme iron enzyme containing a typical low-spin Fe(III) site, (ii) the axial position of the Fe(III) site in the enzyme may be occupied by aquo and sulfhydryl groups, and (iii) aliphatic nitrile substrates directly bind to the Fe(III)-active center through H20-substrate replacement. The NHase also seems to contain pyrroloquinoline quinone (PQQ) or a PQQ-like compound [53]. 

Isolated oxidoreductases always depend on cofactors for the transfer of electrons. Enzyme groups which are well characterized with respect to their biochemistry are those requiring the nicotinamide coenzymes NAD or NADP, the flavins FAD or FMN and the ortho-quinoids such as pyrroloquinoline quinone (PQQ) or trihydroxy-phenylalanine (TOPA). 

Willner et al. [52] have created some elegant interfacial supramolecular assemblies to address this issue by removing the non-covalently bound flavin adenine dinucleotide (FAD) redox center from glucose oxidase and immobilizing the enzyme on a tether consisting of cystamine chemisorbed on a gold surface, a pyrroloquinoline quinone (PQQ) link and FAD. The mediator potential and electron transfer distances of this assembly were carefully chosen so that transfer of electrons from the FAD to the PQQ and to the electrode is very fast. A maximum rate of 900 150 s-1 for the enzymatic reaction within this monolayer assembly was obtained, which is indistinguishable from the value of about 1000 s-1 obtained for the enzyme in solution. While monolayers can offer molecular-level control of the interfacial structure, the... 

Indole alkaloids are derived from tr)y)tophan, which is formed in the shiki-mate pathway. In the case of the terpenoid indoles, tryptophan is usually first converted to tiyptamine by the enzyme tryptophan decarboxylase (TDC) (Fig. 2.9). This enz)une occurs in the cytosol and has been detected in all parts of the developing seedling and in cell cultures of C. roseus (De Luca, 1993). If appears to be a pyridoxoquinoprotein, as two molecules of pyridoxal phosphafe and two molecules of covalently bound pyrroloquinoline quinone were found per enz)une molecule (Pennings et al, 1989). A tdc cDNA clone has been isolafed by immunoscreening of a C. roseus cDNA expression library (De... 

The third case for likely enzymatic generation of an a-cyclopropyl radical or a cyclopropanone equivalent leading to target enzyme destruction is in the oxidation of cyclopropanol by certain bacterial alcohol dehydrogenases which have a novel type of redox coenzyme stoichiometrically bound and required for catalysis. The coenzyme has been termed pyrroloquinoline quinone (PQQ) (174) or methoxatin and the trivial name... 

Integrated electrically-contacted enzyme electrodes were prepared by the surface reconstitution of different apo-enzymes on electrode surfaces. The pyrroloquinoline quinone, PQQ, (7), was covalently linked to a cystamine monolayer associated with an Au-electrode, and A -(2-aminoethyl-FAD), (8), was covalently attached to the PQQ units. Fig. 3-4A. The integrated enzyme-electrode was then prepared by the reconstitution of apo-GOx on the FAD units. The surface coverage of the PQQ-FAD units was estimated to be 5.5x10 ° mole cnr. whereas the surface coverage of the reconstituted... 

Redox proteins that include quinone cofactor units play important roles in biological ET processes. Some of the quinoproteins include the quinone cofactor in a non-covalently linked configuration, such as the pyrroloquinoline quinone, PQQ, dependent enzymes, whereas other quinoproteins include the quinone cofactor covalently-linked to the protein, for example topaquinone (2,4,6-trihydroxyphenylalanine quinone, TPQ) dependent enzymes. A number of quinoproteins include in addition to the quinone cofactor an ET cofactor unit in another protein subunit. These cofactors may be metal ions or a cytochrome-type heme cofactor such as D-fructose dehydrogenase that is a heme containing PQQ-dependent enzyme. ... 

This method was applied to assemble integrated electrically-contacted NAD(P)-dcpcndcnt enzyme electrodes. The direct electrochemical reduction of NAD(l ) cofactors or the electrochemical oxidation of NAD(P)H cofactors are kineticaUy unfavored. Different diffusional redox mediators such as quinones, phenazine, phenoxazine, ferrocene or Os-complexes were employed as electrocatalysts for the oxidation of NAD(P)H cofactors An effective electrocatalyst for the oxidation of the NAD(P)H is pyrroloquinoline quinone, PQQ, (7), and its immobilization on electrode surfaces led to efficient electrocatalytic interfaces (particularly in the presence of Ca ions) for the oxidation of the NAD(P)H cofactors. This observation led to the organization of integrated electrically contacted enzyme-electrodes as depicted in Fig. 3-20 for the organization of a lactate dehydrogenase electrode. 

After the identification of the 13th vitamin, vitamin B12, in 1948, there was a gap of 55 years before the 14th, a pyrroloquinoline quinone (PQQ), previously known and named methoxatin as a redox enzyme cofactor in bacteria, was shown, in 2003, to be a human dietary requirement. 

Dehydrogenases, classified under E.C.1.1., are enzymes that catalyze reduction and oxidation of carbonyl groups and alcohols, respectively I5l The natural substrates of the enzymes are alcohols such as ethanol, lactate, glycerol, etc. and the corresponding carbonyl compounds, but unnatural ketones can also be reduced enantiose-lectively. To exhibit catalytic activities, the enzymes require a coenzyme most of the dehydrogenases use NADH or NADPH, and a few use flavin, pyrroloquinoline quinone, etc. The reaction mechanism of the dehydrogenase reduction is as follows ... 

Some enzymes use other cofactors, e.g., pyrroloquinoline quinone (methoxatin). which has been found in methanol dehydrogenase and several other bacterial dehydrogenases in recent years325. 

Qjiinoproteins are a class of enzymes with cofactors possessing a quinone moiety, which participates directly in catalysis. Several dehydrogenases have been characterized which possess the dissociable cofactor 4,5-dihyro-4,5-dioxo-l-H-pyrrolo[2,3-f quinoline-2,7,9-tricarboxylic acid, which is now commonly called pyrroloquinoline quinone or PQCi. ° Earlier, several other enzymes were believed to possess covalently attached PQCJ as a cofactor. This is now known to be false and an unfortunate consequence of erroneous analytical techniques. Although there are no examples of enzymes possessing covalently bound PQft, covalent quinoproteins with other protein-derived quinones have been identified. 

A number of enzymes which catalyze oxidation reactions, including mammalian lysyl and plasma amine oxidases and bacterial alcohol dehydrogenases, have been determined to utilize pyrroloquinoline quinone (PQQ, methoxatin) as a cofactor (Duine et al., 1987). Substrates of the amine oxidases appear to be activated for a-proton abstraction by formation of a Schiff base with PQQ, fol-... 

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