Figure 2.

A–D: Respiratory ratios are illustrated for the relative contribution of metabolism of electron transport system complex I (CI) and electron transport system complex (CII) substrates, respectively, in patients with Huntington's disease (HD) compared with controls. E,F: The function of pyruvate dehydrogenase was assessed by comparing the ratio of the respiration associated with ATP synthesis by oxidative phosphorylation (OXPHOS) for CI with the addition of ADP and the OXPHOS for CI with the addition of glutamate (OXPHOS_{CI [ MP ]}/OXPHOS_{CI [ MPG ]}) between HD patients and controls. If pyruvate dehydrogenase is rate‐limiting to the mitochondrial respiration for patients with HD, then an increase in respiration should be seen by the addition of glutamate, yielding a low ratio. Quite the contrary, an increased ratio compared with controls was seen in platelets, and no difference could be detected in peripheral blood mononuclear cells (PBMCs). Data are presented as medians and ranges of ratios. ETS, respiration associated with maximal protonophore stimulated flux through the electron transport system; TFC, total functional capacity.