PQQ and quinoprotein research--the first decade

Area of Science:

• Enzymology and biochemistry
• Cofactor research
• Molecular biology

Background:

• Quinoproteins, enzymes containing pyrroloquinoline quinone (PQQ), are prevalent in bacteria and mammals.
• PQQ functions as a versatile cofactor in various enzymatic reactions beyond oxidation.
• The discovery of PQQ has led to re-evaluation of previously characterized enzymes.

Purpose of the Study:

• To review the novel field of PQQ and quinoproteins.
• To discuss the occurrence, function, and biosynthesis of PQQ.
• To explore the implications of PQQ's in situ synthesis for its classification as a vitamin.

Main Methods:

• Review of existing literature on PQQ and quinoproteins.
• Analysis of PQQ's role in different enzymatic reactions.
• Discussion of PQQ biosynthesis pathways in bacteria.
• Consideration of methods for PQQ detection and detachment.

Main Results:

• PQQ is found in diverse enzymes across bacterial and mammalian kingdoms.
• Eukaryotic quinoproteins feature covalently bound PQQ, while bacterial enzymes may utilize free PQQ.
• Biosynthesis of PQQ in methylotrophic bacteria involves tyrosine and glutamic acid precursors.
• Evidence suggests PQQ may be synthesized in situ within quinoproteins, particularly in E. coli.
• Positive effects of PQQ administration in animal models have been reported.

Conclusions:

• PQQ is a widespread and versatile cofactor with diverse enzymatic roles.
• The potential for in situ synthesis challenges the classification of PQQ as a vitamin.
• Further research using advanced detection methods is needed to understand PQQ uptake and processing.