Topaquinone

The deamination of primary amines such as phenylethylamine by Escherichia coli (Cooper et al. 1992) and Klebsiella oxytoca (Flacisalihoglu et al. 1997) is carried out by an oxidase. This contains copper and topaquinone (TPQ), which is produced from tyrosine by dioxygenation. TPQ is reduced to an aminoquinol that in the form of a Cu(l) radical reacts with O2 to form H2O2, Cu(ll), and the imine. The mechanism has been elucidated (Wihnot et al. 1999), and involves formation of a Schiff base followed by hydrolysis in reactions that are formally analogous to those involved in pyridoxal-mediated transamination. 

Several lupin alkaloids have been derived from the unsaturated quinalozidine 433, that was obtained in the treatment of amine 431 with ortho-quinone 432. This quinone behaves as a model of topaquinone, the cofactor of copper-containing amine oxidases. The cyclization step involved a nucleophilic attack of the piperidine nitrogen of 431 onto a side-chain aldehyde function that is unmasked by the oxidative deamination. Quinolizine 433, when treated with dehydropiperidine, gave the oxime ether 434 that, on ozonolysis followed by reduction, afforded sparteine 10, presumably via the bis(iminium) system 435 (Scheme 102) <1996JOC5581>. 

This enzyme [EC 1.4.99.3], also known as amine dehydrogenase and primary-amine dehydrogenase, catalyzes the reaction of R-CH2-NH2 with water and an acceptor to produce R-CHO, ammonia, and the reduced acceptor. Tryptophan tryptophylquinone (TTQ) is the cofactor for this enzyme. See Resonance Raman Spectroscopy Topaquinone... 

Hydoxylated amino acid residues that participate in redox-active enzyme reactions. See Topaquinone... 

METHYLAMINE DEHYDROGENASE N-METHYLCLUTAMATE SYNTHASE METHYLAMINE DEHYDROGENASE RESONANCE RAMAN SPECTROSCOPY TOPAQUINONE... 

ENZYME KINETIC EQUATIONS REDOX-ACTIVE AMINO ACIDS TOPAQUINONE REDOX POTENTIAL Redox reactions,... 

BIOCHEMICAL NOMENCLATURE TOLUENE DIOXYGENASE TONICITY TOPAQUINONE... 

Topaquinone-containing enzymes, REDOX-ACTIVE AMINO ACIDS... 

Copper-containing amine oxidases (non-blue copper proteins) catalyze the oxidative deamination of primary amines to the corresponding aldehydes with the release of ammonia and concomitant reduction of oxygen to hydrogen peroxide. They typically use a quinone redox cofactor [topaquinone (TPQ)], which is bound covalently in the active site, and are thought to form a Cu(I)-TPQ semi-quinone radical intermediate during the redox reaction [13]. 

Topaquinone (TPQ). Both bacteria and eukaryotes contain amine oxidases that utilize bound copper ions and 02 as electron acceptors and form an aldehyde, NH3, and H202. The presence of an organic cofactor was suggested by the absorption spectra which was variously attributed to pyridoxal phosphate or PQQ. However, isolation from the active site of bovine serum... 

Lysine tyrosylquinone (LTQ). Another copper amine oxidase, lysyl oxidase, which oxidizes side chains of lysine in collagen and elastin (Eq. 8-8) contains a cofactor that has been identified as having a lysyl group of a different segment of the protein in place of the - OH in the 2 position of topaquinone.465 Lysyl oxidase plays an essential role in the crosslinking of collagen and elastin. 

Topaquinone (TPQ) 816, 817s Topoisomerases 219,575, 638, 657,659 Topological theory of graphs 466 Topologies... 

Topaquinone (TPQ), the oxidized form of 2,4,5-trihydroxyphenylalanine (TOPA), is the cofactor of copper-containing amine oxidases. The following model compounds have been prepared in order to understand the catalytic function of TPQ the jV-pivaloyl derivative of 6-hydroxydopamine in aqueous acetonitrile [38] topaquinone hydantoin and a series of 2-hydroxy-5-alkyl-l,4-benzoquinones in anhydrous acetonitrile (o- as well as />-quinones) [39] 2-hydroxy-5-methy 1-1,4-benzoquinone in aqueous system [40] and 2,5-dihydroxy-1,4-benzoquinone [41]. Reaction of model compounds with 3-pyrrolines revealed why copper-quinopro-tein amine oxidases cannot oxidize a secondary N [42], The studies clearly showed that certain model compounds do not require the presence of Cu for benzylamine oxidation whereas TPQ does [38,40] the aminotransferase mechanism proceeds via the -quinone form [39] the 470 nm band can be ascribed to a 71-71 transition of TPQ in />-quinonic form with the C-4 hydroxyl ionized but hydrogen bonded to some residue [40] hydrazines attack at the C-5 carbonyl, forming an adduct in the azo form [41], Electrochemical characterization has been carried out for free TPQ [43],... 

Topaquinone and lysyltopaquinone are formed by postsynthetic modification of the precursor proteins of the active enzymes. A tyrosine residue in the enzyme undergoes autocatalytic oxidation in the presence of enzyme-bound copper and oxygen. Lysyltopaquinone in lysyl oxidase is believed to be synthesized by reaction between topaquinone and the e-amino group of a lysine residue to form the cross-linked imino adduct. This means that it is highly improbable that either topaquinone or lysyltopaquinone is a dietary essential, because there is no way in which preformed quinone could be incorporated into the precursor protein or a hypothetical apoenzyme. 

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