| Popis: |
The current narrative that the reduced coenzymes NADH and FADH2 feed electrons from the tricarboxylic acid cycle into the mitochondrial electron transfer system creates ambiguities around respiratory Complex II (CII). The succinate dehydrogenase subunit SDHA of CII oxidizes succinate and reduces covalently bound FAD to FADH2 in the canonical forward tricarboxylic acid cycle. However, several graphical representations of the membrane-bound electron transfer system (ETS) depict FADH2 in the mitochondrial matrix to be oxidized by CII. This leads to the false conclusion that FADH2 feeds electrons into the ETS through CII, including FADH2 from the tricarboxylic acid cycle and the β-oxidation cycle in fatty acid oxidation. In reality, FAD and succinate are the substrates of SDHA at the ETS-entry into CII. The reduced flavin groups FADH2 and FMNH2 are products downstream within CII and CI, respectively. Further electron transfer converges at the coenzyme Q-junction. Similarly, electron transferring flavoprotein and mitochondrial glycerophosphate dehydrogenase feed electrons into the Q-junction but not through CII. The ambiguities surrounding Complex II in the literature and educational tools call for quality control, to secure scientific standards in current communications on bioenergetics and ultimately support adequate clinical applications. |
