Figure 1.

Schematic representation of different metabolic processes involved in cellular energy metabolism. (a) shows the interrelationships between the oxidative pathways of glucose, aminoacid, and fatty acid, which lead to ATP production in the mitochondrial RC enzymes (black box). White lines illustrate the electron flow through CoQ₁₀ in the RC. Dashed lines indicate substrates that generate abnormal metabolites in mitochondrial cytopathies (i.e., lactate, alanine, organic acids, and acyl-carnitines). (b) shows the enzymatic cascade for the biosynthesis of CoQ₁₀ from mevalonic acid (left) and the principal mitochondrial enzymes with antioxidant function (right): (1) superoxide dismutase, (2) thioreductase, (3) glutathione peroxidase, (4) catalase, (5) Fenton reaction, (6) prenyl diphosphate synthetase subunit 1 and 2 (PDSS1 and PDSS2), and (7) CoQ biosynthesis enzymes (COQ2–COQ8).