FIG. 2.

Function of mitochondrial enzymes in COX10 KO cells. (A) Total cell respiration of COX10 KO cells was determined by the rate of oxygen consumption on a Clark O₂ electrode. Knockout clones (K11, K18, and K19) did not respire, either with endogenous substrates or with ascorbate-TMPD, which donates electrons directly to complex IV. (B) Respiratory complex activities of COX10 KO cells. Enzymatic activities were measured spectrophotometrically in isolated mitochondria. Specific activities, initially obtained as micromoles/minute/milligram, are expressed as ratios to citrate synthase activity. Error bars represent standard deviations of at least six independent measurements. (C) Cytochrome spectra of COX10 KO cells. The differential oxidized spectra minus reduced spectra for C12 and K11 mitochondrial cytochromes are shown. The COX10 KO clone K11 lacked the cytochrome a and a₃ peak at 603 nm. cyt, cytochrome; Ctrl, control.