ABSTRACT
At this point it became clear that the reference to quinoproteins as enzymes that possessed Pyrroloquinoline quinone (PQQ) would have to be reevaluated. It was apparent that while many enzymes classified as quinoproteins didpossess PQQ, some of these enzymes, particularly those with covalently bound prosthetic groups, possessed instead other previously unrecognized and novel quinone species at their active sites. A peculiar and very interesting observation regarding prokaryotic quinoproteins is that in many bacteria the synthesis of the apoenzyme and PQQ is not coordinate. Regarding the physiological relevance of PQQ to mammals and other eukaryotes, the sum of the evidence accumulated in the past few years clearly indicates that PQQ and related compounds are capable of exerting a variety of effects in mammalian systems. The field of quinoprotein research is relatively young, and the body of information on quinoproteins and quinone cofactors and prosthetic groups, particularly PQQ, is growing at an increasingly rapid rate.
