Pyrroloquinoline quinone (PQQ), also called methoxatin, is a redox cofactor. It is found in soil and foods such as kiwifruit, as well as human breast milk. Enzymes containing PQQ are called quinoproteins. Glucose dehydrogenase, one of the quinoproteins, is used as a glucose sensor. PQQ stimulates growth in bacteria.
The scientific journal Nature published the 2003 paper by Kasahara and Kato that essentially stated that PQQ was a new vitamin and in 2005, an article by Anthony and Fenton that stated that the 2003 Kasahara and Kato paper drew incorrect and unsubstantiated conclusions. An article in The Proceedings of the National Academy of Sciences in 2018 identified pyrroloquinoline quinone as a “longevity vitamin” not essential for immediate survival, but necessary for long-term health.