Quinoprotein enzymes

Sutcliffe, M.J. and Scrutton, N.S. (2002). A new conceptual framework for enzyme catalysis. Hydrogen tunnelling coupled to enzyme dynamics in flavoprotein and quinoprotein enzymes. Eur. J. Biochem. 269, 3096-3102... 

Quinoproteins, enzymes containing quinoid cofactors, e.g., pyrroloquino-linequinone and triptophanequinone 91MI35. 

We have recently reviewed our work on quinoprotein enzymes elsewhere [42]. In this chapter we review our studies of H-tunneling in flavoprotein enzymes. 

Anthony C. Pyrroloquinoline quinone (PQQ) and quinoprotein enzymes. Antioxid Redox Signal 2001 3 757-774. 

Davis G, Hill HAG, Aston WJ, Higgins IJ, Turner APR 1983. Bioelectrochemical fuel cell and sensor based on a quinoprotein, alcohol dehydrogenase. Enzyme Microb Technol 5 383-388. 

At first it appeared that PQQ had a broad distribution in enzymes, including eukaryotic amine oxidases. However, it was discovered, after considerable effort, that there are additional quinone cofactors that function in oxidation of amines. These are derivatives of tyrosyl groups of specific enzyme proteins. Together with enzymes containing bound PQQ they are often called quinoproteins.11, 1... 

Pyrroloquinolinequinone (213) (2,7,9-tricarboxy-l/7-pyrrolo[2,3-/]quinoline-4,5-dione, PQQ) (trivial name methoxatin) has been identified as a co-factor in many enzymes, including those that oxidize MeOH to HCHO in methylotrophic and autotrophic bacteria. Quinoproteins appear in mammalian systems as well, and methoxatin itself (213) has even been identified as an inhibitor of HIV-1 reverse transcriptase (for PQQ reviews, see <91MI 722-02, 95MI 722-02)). Interest in under-... 

Flavin oxidases include d- and l-amino acid oxidases, and some amine oxidases, although others are quinoproteins (Section 9.8.3). In these enzymes, the flavin is reduced by dehydrogenation of the substrate, byway of an intermediate substrate-flavin adduct, as occurs in the dehydrogenases (Section 7.3.3). 

Goodwin, M. G., Avezoux, A., Dales, S. L., and Anthony, C., 1996, Reconstitution of the quinoprotein methanol dehydrogenase from active Ca -free enzyme with Ca, Sr or Ba t Biochem. J. 319 839A842. 

Linster CL, Gomez TA, Christensen KC, Young BD, Brenner C. Arabidopsis VTC2 encodes a GDP-L-galactose phosphorylase, the last unknown enzyme in the Smirnoff-Wheeler pathway to ascorbic acid in plants. J. Biol. Chem. 2007 282 18879-18885. Davidson VL. Electron transfer in quinoproteins. Arch. Biochem. Biophys. 2004 428 32-40. 

The majority of the electrochemical investigations of quinoproteins focus on the understanding of the mechanism and biological function of these enzymes. The enzymes find application in mediated biosensors for the main substrates of these enzymes and the measurement of redox dyes and phenohc compounds. The few cases of DET of these en mes for biosensor applications are presented here. 

MPO from H. niger was isolated and its molecular weight determined by gel filtration (135 kDa) and the SDS-PAGE analysis showed that the enzyme is a dimmer [140]. MPO has also been obtained from other plant speeies such as D. stramonium [141] and N. tabacum [142], Inhibition studies of Hyoscyamus MPO demonstrated the quinoprotein characteristic of this enzyme [140], a feature previously reported for N. tabacum MPO, after conducting a suicidal inhibition of the enzyme with phenyUiydrazine [143]. 

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