The PQQ story

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• The cofactor pyrroloquinoline quinone (PQQ) was discovered approximately twenty years ago.
• Quinoproteins, enzymes utilizing quinone cofactors, are primarily involved in oxidation reactions of alcohols, sugars, and amines.

Purpose of the Study:

• To provide a personal perspective on the delayed discovery of PQQ and its identification process.
• To review the physiological significance of PQQ and the discovery of related quinone cofactors (TPQ, TTQ, LTQ).
• To discuss the implications of quinoprotein research for enzyme applications and cofactor diversity.

Main Methods:

• Review of historical data and personal insights into the discovery of PQQ.
• Analysis of the literature on quinoprotein function, classification, and applications.
• Comparative analysis of different enzyme systems catalyzing similar reactions.

Main Results:

• The discovery of PQQ led to the identification of three additional quinone cofactors (TPQ, TTQ, LTQ) integrated into protein structures.
• PQQ-containing enzymes are involved in bacterial oxidation processes, such as vinegar production and glucose conversion.
• Soluble glucose dehydrogenase, a PQQ-containing enzyme, is vital for glucose monitoring in diabetic patient blood samples.
• Quinohemoprotein alcohol dehydrogenases exhibit enantiospecificity valuable for synthesizing chiral compounds.
• Quinoproteins broaden the catalytic repertoire for biochemical reactions, offering more application possibilities.

Conclusions:

• Quinoprotein research has expanded the understanding of enzyme diversity and catalytic capabilities.
• The discovery of PQQ and other quinone cofactors highlights the role of amino acids in cofactor formation, beyond nucleotides.
• Despite initial hopes, PQQ is primarily found in bacteria, diminishing its potential as a human vitamin.
• Further discoveries of novel quinone cofactors are anticipated.