Pyrroloquinoline Quinone

Pyrroloquinoline quinone (PQQ) was discovered by J.G. Hauge as the third redox cofactor after nicotinamide and flavin in bacteria (although he hypothesised that it was naphthoquinone). Anthony and Zatman also found the unknown redox cofactor in alcohol dehydrogenase and named it methoxatin. In 1979, Salisbury and colleagues as well as Duine and colleagues extracted this prosthetic group from methanol dehydrogenase of methylotrophs and identified its molecular structure. Adachi and colleagues identified that PQQ was also found in Acetobacter.

These enzymes containing PQQ are called quinoproteins. Glucose dehydrogenase, one of the quinoproteins, is used as a glucose sensor. Subsequently, PQQ was found to stimulate growth in bacteria. In addition, antioxidant and neuro-protective effects were also found.

PQQ biosynthesis in bacteria begins with protein biosynthesis to make a short peptide, PqqA, on the ribosome. All atoms in PQQ derive from a glutamic acid and a tyrosine in PqqA, which become linked initially by the radical SAM enzyme PqqE .

In 1989, Rucker and colleagues reported that mice deprived of PQQ showed various abnormalities, and it was suggested that PQQ may also have an important nutritional role in other mammals. In 2003, it was reported that aminoadipate semialdehyde dehydrogenase (AASDH) might also use PQQ as a cofactor, suggesting a possibility that PQQ is a vitamin in mammals. Rucker and colleagues concluded that insufficient information is available so far to state that PQQ is a vitamin for mammals, although PQQ may be an important biological factor.

It was recently shown that PQQ may stimulate growth of plants (cucumbers and tomatoes) in hydroponic culture and may be the causative factor in plant growth stimulation by a strain of Pseudomonas fluorescens bacterium.

PQQ as a prosthetic group on glucose dehydrogenase has been utilized at the anode in an enzyme based fuel cell.