Chemical Behavior of Coenzyme PQQ toward Aminoguanidine: Redox Reaction and Adduct Formation

The reaction of coenzyme PQQ with aminoguanidine, which is known as an inhibitor of quinoprotein amine oxidases, was investigated in vitro. The redox reaction predominantly proceeded at pH 10.0 to give PQQH2 (quinol), whereas deactivation of PQQ occurred at pH 6.7 to give the triazine adduct. In the case of semicarbazide or acetohydrazide as the substrate, azo adduct formation was mainly observed even at pH 10.0. Importance of the C-5 carbinolamine-type intermediate a is discussed.