[6] A novel aspect of PQQ is its biosynthesis in bacteria from a ribosomally translated precursor peptide, PqqA (UniProt P27532).

[9] Efforts to understand PQQ biosynthesis have contributed to broad interest in radical SAM enzymes and their ability to modify proteins, and an analogous radical SAM enzyme-dependent pathway has since been found that produces the putative electron carrier mycofactocin, using a valine and a tyrosine from the precursor peptide, MftA (P9WJ81).

[11] Although quinoproteins are mostly found in bacteria, a Coprinopsis cinerea (fungus) pyranose dehydrogenase has been shown to use PQQ in its crystal structure.

The mammalian lactate dehydrogenase requires PQQ to run but uses NADH as the direct redox cofactor.

[13] An article by Bruce Ames 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.