Pyrroloquinoline quinone (henceforth pqq) is a small quinone molecule which

has the ability to be a redox agent, capable of reducing oxidants (an antioxidant

effect) and then being recycled by glutathione back into an active form. It appears

to be quite stable as it can undergo several thousand cycles before being used up,

and it is novel since it associates with protein structures inside the cell (some

antioxidants, mostly notably carotenoids like β-carotene and Astaxanthin, are

located at specific areas of a cell where they exert proportionally more antioxidant

effects due to proximity; PQQ seems to do this near proteins like carotenoids do so

at the cell membrane).