SLIRP regulates the rate of translation but is not essential for respiratory chain activity.

<p>(A) Mitochondrial translation rate assessed by <i>in cellulo</i>³⁵S-methionine/cysteine pulse labelling for 10, 30 and 60 minutes in wild-type (<i>Slirp</i>^+/+) and <i>Slirp</i> homozygous knockout (<i>Slirp</i>^-/-) primary MEFs. (B) Mitochondrial translation rate assessed by <i>in organello</i>³⁵S-methionine pulse labelling for 10, 30 and 60 minutes in isolated heart and liver mitochondria from 12-week old <i>Slirp</i>^+/+ and <i>Slirp</i>^-/- mice. (C) Steady-state levels of the mitochondria- and nucleus-encoded subunits of the respiratory chain complexes as assessed by western blot analysis of protein extracts from heart and liver mitochondria from 12-week old <i>Slirp</i>^+/+ and <i>Slirp</i>^-/- mice. (D) Oxygen consumption rate of isolated liver mitochondria from 12-week old <i>Slirp</i>^+/+ (white bars) and <i>Slirp</i>^-/- (black bars) mice. Isolated mitochondria were incubated with complex I or complex II substrates. Each set of substrates was successively combined with ADP (to assess the phosphorylating respiration), oligomycin (to assess the non-phosphorylating respiration) and CCCP (to assess uncoupled respiration). n = 3. Error bars represent SEM. (E) Activity of the respiratory chain complexes I (CI), II (CII) and IV (CIV) of liver mitochondria from 12-week old <i>Slirp</i>^+/+ and <i>Slirp</i>^-/- mice. Citrate synthase activity (CS) was used as a control. n = 3. Error bars represent SEM.