Figure 2.

Enzymatic regulation of the PDH complex. The PDH complex is multienzyme complex comprising three major enzymes, including PDH (enzyme 1 [E1]), dihydrolipoyl acetyltransferase (DLAT or E2), and dihydrolipoyl dehydrogenase (DLD or E3). PDH is responsible for the decarboxylation of pyruvate, and is tightly controlled by phosphorylation, whereby 4 isoforms of PDHK phosphorylate/deactivate PDH, and 2 isoforms of PDHP dephosphorylate/activate PDH. PDHK is positively regulated by increased acetyl CoA/CoA and NADH/NAD⁺ ratios, whereas increases in pyruvate inhibit PDHK but stimulate PDHP. In addition, increases in mitochondrial calcium and magnesium concentrations can also stimulate PDHP.