Add time:08/31/2019         Source:sciencedirect.com

Publisher SummaryPyrroloquinoline quinone (PQQ, 2,7,9-tricarboxy-1H-pyrrolo[2,3-f]quinoline- 4,5-dione) is one of the quinone cofactors functioning in the so-called quinoprotein enzymes. This chapter discusses the isolation, preparation, and assay of PQQ. PQQ functions only as a cofactor in bacterial dehydrogenases catalyzing the oxidation of alcohols or sugars. Covalently bound quinone cofactors are topaquinone and tryptophyltryptophan quinone, which derive from oxidized specific tyrosine and tryptophan residues in the protein chain of the enzymes to which they belong, respectively. The chapter describes the synthesis of several substituted PQQs (with alkyl groups at the N-1, C-3, or C-8 position), of 6-deaza-PQQ, and of decarboxy- PQQs. In addition, the o-quinone moiety of PQQ is modified by reduction or derivatization. The biological activity of some of these analogs is investigated. PQQ, a compound with three carboxylic acid groups, is water soluble when these groups are deprotonated. In principle, anion-exchange chromatography is feasible to detect and determine the compound. A method has been developed in which the PQQ in the sample and added labeled PQQ are chemically modified and the product is investigated by gas chromatography–mass spectrometry (GC–MS). The levels found with this assay in plant materials are orders of magnitude lower than those found with the redox-cycling assay.

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