Figure 2.

Oxidative metabolism, oxidative phosphorylation (OXPHOS), and reactive oxygen species (ROS) generation. NADH is mainly produced by glycolysis, pyruvate decarboxylase complex (PDC), fatty acid β-oxidation (FAO), and tricarboxylic acid (TCA) cycle to fuel electron transportation chain (ETC) via complex I, whereas FADH₂ is mainly produced by FAO and TCA cycle and fuels ETC via complex III. Glycerol-phosphate and malate-aspartate shuttle mechanisms serve to transfer reducing equivalents through the outer mitochondrial membrane from the cytoplasm to ETC. Superoxide anion radical, a primary type of ROS, is produced as a byproduct of ETC.