Pyrroloquinoline quinone-dependent dehydrogenase (PQQ-DH) (PQQ-DH)

Pyrroloquinoline quinone-dependent dehydrogenases (PQQ-DHs) are a specialized class of oxidoreductases, also known as quinoproteins, that utilize the redox-active cofactor pyrroloquinoline quinone (PQQ) to catalyze the oxidation of various substrates including alcohols, sugars, and amines (Matsushita et al., 2002). These enzymes are primarily located in the periplasmic space of Gram-negative bacteria, where they facilitate the initial steps of substrate oxidation and channel electrons directly into the respiratory chain, often bypassing the need for NAD(P)+ (Klinman & Bonnot, 2014). A prominent member of this family is PQQ-dependent glucose dehydrogenase (GDH-PQQ), which has been extensively utilized in the development of blood glucose monitoring systems due to its high catalytic efficiency and lack of oxygen interference (FDA, 2009). While PQQ-dependent enzymes are not natively expressed in humans, PQQ itself is found in human tissues and breast milk, leading to its investigation as a potential bioactive compound with neuroprotective and antioxidant properties (UniProt). From a therapeutic perspective, these enzymes represent potential targets for the development of novel antibacterial agents designed to disrupt bacterial energy metabolism. However, a significant clinical challenge associated with GDH-PQQ-based diagnostics is the lack of substrate specificity, which historically led to life-threatening errors in glucose readings for patients receiving treatments containing maltose or icodextrin (FDA, 2009).

Other names

Quinoprotein dehydrogenasePQQ-containing dehydrogenaseMethoxatin-dependent dehydrogenaseGlucose dehydrogenase (PQQ-dependent)

These enzymes catalyze the oxidation of substrates (such as glucose or alcohols) by transferring two electrons and two protons to the PQQ prosthetic group to form PQQH2; the reduced cofactor is then re-oxidized by transferring electrons to an external acceptor, typically a cytochrome or ubiquinone, within the bacterial electron transport chain (Matsushita et al., 2002).