Catalase E and

Several biochemical processes in mammals are dependent on the redox-active o-quinone, https://www.https://www. ( quinone enhances the conversion of lactate to pyruvate in the presence of NAD+. may also modulate the function of cellular LDH. Nevertheless, the underlying molecular mechanisms are not well established. Consequently, future studies will need to determine the contribution of the enzymatic reaction to important nutritional functions.

The cellular LDH is a homo- or heterotetrameric enzyme that converts pyruvate generated in glycolysis to l-lactate. LDH is encoded by two related genes, LDH-A and LDH-B. In the absence of NAD+, the activity of LDH was not significantly increased. However, LDH activity was significantly enhanced. Moreover, oxidative phosphorylation in the TCA cycle and cytochrome c oxidase activities were enhanced in Hepa1-6 cells exposed to PQQ for 24 or 48 h.

To identify proteins that bind to PQQ, PQQ-immobilized Sepharose beads were used. These beads were subjected to tryptic digestion and subsequently analyzed by nano-LC-ESI-Q-TOF-MS/MS. It was discovered that six proteins were putatively identified as mammalian PQQ-binding proteins. These proteins included a translation elongation factor, peroxiredoxin, and antioxidant enzymes. Arg-98, an amino acid residue involved in substrate binding, was conserved in both mouse and rabbit LDH-A.

Docking studies revealed that the PQQ moiety was situated close to the reduced nicotinamide moiety of NADH. PQQ was also found to overlap protein-bound NADH. The PQQ-binding protein was located within the active site pocket of LDH-A. This was demonstrated by docking simulations using the MOE software.