Pyrroloquinoline Quinone (PQQ)

PQQ (Pyrroloquinoline quinone: 4,5-dihydro-4,5-dioxo-1Hpyrrolo-[2,3-f] quinoline- 2,7,9-tricarboxylic acid) is a prosthetic group of certain dehydrogenases, redox active substance which can accept one or two electron(s) in redox cycle, and shows several different bioactivities on bacteria, plants, and mammals. This compound was found as the third redox cofactor in quinoprotein glucose dehydrogenase after nicotinamide and flavin cofactors in bacteria. Salisbury and colleagues as well as Duine and colleagues extracted this prosthetic group from quinoprotein methanol dehydrogenase of methylotrophs and identified its molecular structure by X-ray crystallographic analysis, named it methoxatin and PQQ, respectively. Ameyama and colleagues identified that PQQ was also found in other oxidative bacteria. These enzymes containing PQQ are called quinoproteins. Glucose dehydrogenase, one of the quinoproteins, is used for a glucose biosensor. Subsequently, PQQ was found to stimulate growth in bacteria. Effect of PQQ on mammals was first reported by Killgore et al, although no enzymes having PQQ as a cofactor in mammals have been identified yet. In addition, several physiological activities including antioxidant and neuro-protective effects were also reported.