Cofactor quinone

Cooper RA, PE Knowles, DE Brown, MA McGuirl, DM Dooley (1992) Evidence for copper and 3,4,6-trihy-droxyphenylalanine quinone cofactor as an amine oxidase from Gram-negative Escherichia coli K-12. Biochem J 288 337-340. 

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... 

Tryptophan tryptophanylquinone (TTQ). This recently discovered quinone cofactor is similar to the lysyl tyrosylquinone but is formed from two trypto-phanyl side chains.466 It has been found in methyl-amine dehydrogenase from methylotrophic gramnegative bacteria467-469 and also in a bacterial aromatic amine dehydrogenase.470... 

When FI is replaced by PQQ (pyrroloquinolinequinone), a novel heterocyclic o-quinone cofactor that was first isolated and identified from methanol dehydrogenase of methylotrophic bacteria in 1979 [68], the photochemical oxidation of benzyl alcohols occurs efficiently without HC104 in MeCN [69] ... 

Pyrroloquinoline quinone, and probably also the other quinone cofactors, can be considered to be medium-potential oxidants (Em PQQ/PQQH2, 0.09 V (NHE) aq., pH 7), as distinguished from high-potential quinones that are of use as oxidants in organic synthesis [13], In addition, PQQ will resist competing nucleophilic 1,4-additions of organic reductants as is observed with less heavily substituted quinones. 

Cu has a bifunctional role in copper-quinoprotein amine oxidases, catalyzing the formation of TPQ from the specific tyrosy l residue in the precursor protein and playing a role in the catalytic mechanism, most probably with 02 reacting with Cu(I) in the oxidative part of the cycle. The recent discovery of LTQ suggests that other combinations of quinone cofactors may be found in the future. 

Backes, G., Davidson, V. L., Huitema, F., Duine, J. A., and Sanders-Loehr, J., 1991, Characterization of the tryptophan-derived quinone cofactor of methylamine dehydrogenase by resonance Raman spectroscopy, Biochemistry 30 9201n9210. 

Holt, A., Alton, G., Seaman, C. H., Loppnow, G. R., Szpacenko, A., Svendsen, 1., and Palcic, M. M., 1998, Identification of die quinone cofactor in mammalian semicarbazide-sensitive amine oxidase, Biochemistry 37 4946n4957. 

Matsuzaki, R., Fukui, T., Sato, H., Ozaki, Y., and Tanizawa, K., 1994, Generation of the TOPA quinone cofactor in bacterial monoamine oxidase by cupric ion-dependent autooxidation of a specific tyrosyl residue, EEBS Lett. 351 360n364. 

Tanizawa, K., Matsuzaki, R., Shimizu, E., Yorifuji, T., and Fukui, T., 1994, Cloning and sequencing of phenylethylamine oxidase from Arthrobacter globiformis and implication of Tyr 382 as the precursor to its covalently bound quinone cofactor, Biochem. Biophys. Res. Commun. 199 1096nll02. 

Figure 18 Tyrosine-derived quinone cofactors, (a) TPQ, 2,4,5-tri-hydroxyphenylalanine quinone (b) LTQ, lysyl tyrosyl quinone...

Figure 1. Common redox and protonation states for (a) flavin and (b) quinone cofactors.

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. ... 

Figure 4.3. Structures of quinone cofactors. PQQ pyrolloquinoline quinone TPQ 2,4,5-trihydroxyphenylalanine quinone LTQ lysine tyrosylquinone TTQ tryptophan tryptophyl quinone CTQ cysteine tryptophyl quinone. Taken with permission from Mure [2].

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