New Quinocofactors in Eukaryotes

The field of quinoproteins began in the 1980s with the discovery and characterization of a low molecular weight, dissociable cofactor from Gram-negative bacteria, designated pyrroloquinoline quinone (PQQ,%1 Fig. 1 A). PQQ was found to be biologically active both in vitro, via the reconstitution of activity to periplasmic alcohol dehydrogenases, and in vivo, as a stimulant to cell growth. The latter behavior is a consequence of the elevated production of apo-alcohol dehydrogenases relative to PQQ, which could thus be described as a bacterial “vitamin” (cf.