Q

A–D. Complex I‐, II‐, and IV‐dependent respiration by protein (A), MTDR mitochondrial content (B), Complex I‐, II‐, and IV‐dependent respiration corrected by mitochondrial mass (C), and Western blot followed by quantification (D) in heart homogenates from WT and Ndufs4 KO mice. E. Complex I‐, II‐, and IV‐dependent respiration by protein in Polg mutant (Polg MT) and control heart homogenates. F. MTDR mitochondrial content in Polg MT and control heart homogenates. G. Complex I‐, II‐, and IV‐dependent respiration corrected by mitochondrial mass. H. Western blot followed by quantification in heart homogenates from WT (control) and Polg MT mice. I. Quantification of Complex I‐, II‐, and IV‐dependent respiration in zebrafish muscle homogenate from young and old fish. J. Quantification of Complex I‐ and IV‐dependent respiration using RIFS in zebrafish deyolked embryo homogenate acutely treated with rotenone before freezing. K. Complex I to Complex IV ratio in zebrafish deyolked embryo homogenate in the indicated conditions. L. Complex I activity measure spectrophotometrically in zebrafish deyolked embryo homogenate in the indicated conditions. M. Representative H&E sections from human donors show the presence of multilocular adipose tissue in the pheochromocytoma (Pheo) sample. UCP1‐DAB staining (central panels) and Grp75/mortalin fluorescence staining (bottom panels) from control and Pheo patients. N. Western blot followed by quantification in homogenates from control and Pheo patients. O. Complex I‐, II‐, and IV‐dependent respiration by protein in periadrenal adipose tissue homogenates from control and Pheo human patients. P. Mitochondrial content by MTDR quantification in homogenates from control and Pheo human patients. Q. Quantification of complex activities (I, II, and IV) in MAS versus MAS supplemented with Cyt c and ALA buffer in isolated and cryopreserved human monocytes, lymphocytes, and platelets.