Succinate dehydrogenase (Fungal) (SDH)

Fungal succinate dehydrogenase (SDH), also referred to as Complex II or succinate:ubiquinone oxidoreductase, is a critical enzyme complex located in the inner mitochondrial membrane of fungi (UniProt, 2024). It plays a pivotal role in cellular energy metabolism by participating in both the tricarboxylic acid (TCA) cycle and the mitochondrial electron transport chain (PubMed: 31554304). Specifically, it catalyzes the oxidation of succinate to fumarate while simultaneously reducing ubiquinone to ubiquinol. This enzyme is the primary target for a significant class of agricultural fungicides known as Succinate Dehydrogenase Inhibitors (SDHIs), such as boscalid and fluxapyroxad (FRAC, 2023). SDHIs bind to the ubiquinone-binding pocket of the enzyme, effectively blocking electron flow and halting fungal growth. However, the emergence of resistance due to point mutations in the SDH subunits (B, C, or D) remains a major challenge in crop protection and clinical settings (PubMed: 26230537).

Other names

Complex IISuccinate:ubiquinone oxidoreductaseSQRSuccinate-coenzyme Q reductase

Inhibition of the ubiquinone-binding site (Q-site) within the succinate dehydrogenase complex, which prevents the transfer of electrons from succinate to ubiquinone, thereby disrupting the mitochondrial electron transport chain and ATP synthesis (PubMed: 28653305; FRAC, 2023).