Pyrroloquinoline quinone, originally discovered in 1979, was reported to be a vitamin in mice on April 24, 2003 by a research team led by Takafumi Kato of the Japanese Institute of Physical and Chemical Research (http://www.riken.go.jp/engn/index.html) (source (http://www.brain.riken.jp/labs/mdmd/pqq/)). Because it has not been shown that any disease results from a dietary deficiency of this substance in humans, it is not considered a vitamin in humans.
Beta-propeller repeat occurring in enzymes with pyrrolo-quinoline quinone (PQQ) as cofactor, in Ire1p-like Ser/Thr kinases, and in prokaryotic dehydrogenases.
The PQQ is located on the pseudo 8-fold rotation axis of the heavy subunit, in a funnel-shaped internal cavity, sandwiched between the indole ring of Trp237 and the two sulfur atoms of the Cys103-Cys104 vicinal disulfide.
The C5 atom of PQQ could be activated by electrophilic catalysis by a nearby argenine side-chain or by the calcium ion bound to PQQ.
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