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Reassessment of the Active Site Quino-Cofactor Proposed To Occur in the Aspergillus niger Amine Oxidase AO-I from the Properties of Model Compounds

2000; American Chemical Society; Volume: 39; Issue: 25 Linguagem: Inglês

10.1021/bi000507m

1943-295X

Chris R. Melville, Edward L. Green, Joann Sanders–Loehr, Judith P. Klinman,

Porphyrin Metabolism and Disorders

Quino-cofactors have been found in a wide variety of prokaryotic and eukaryotic organisms. Two variants have, thus far, been demonstrated to derive from tyrosine precursors: these are the 2,4,5-trihydroxyphenylalanine quinone (topa quinone or TPQ) [Janes, S. M., et al. (1990) Science 248, 98] and an o-quinone analogue containing the side chain of a lysine residue (lysyltyrosine quinone or LTQ) [Wang, S. Z., et al. (1996) Science 273, 1078]. Additionally, a third variant of the family of tyrosine-derived cofactors has been reported to exist in an Aspergillus niger amine oxidase AO-I. This was described as an o-quinone cross-linked to the side chain of a glutamate residue [Frebort, I. (1996) Biochim. Biophys. Acta 1295, 59]. We have synthesized model compounds related to the proposed structure. Characterization of the redox properties for the model compound and spectral properties of its 4-nitrophenylhydrazine derivative lead us to conclude that the cofactor in A. niger amine oxidase AO-I has been misidentified. A TPQ carboxylate ester is considered an unlikely candidate for a biologically functional quino-cofactor.