Figure 1.

The loss of Ndufs4 causes a mild phenotype in heart. (A) Immunoblots from total (T) and mitochondrial (M) fractions of control and Ndufs4 knockout hearts. (B) Heart-to-body weight ratios in control and Ndufs4 heart knockout mice. (C) Respiratory chain enzyme activities in detergent-permeabilized mitochondrial preparations. Complex I (NADH:coenzyme Q reductase, NQR), complexes I/III (NADH:cytochrome c reductase, NCR), complex II (succinate dehydrogenase, SDH), complexes II/III (succinate:cytochrome c reductase, SCR) and complex IV (cytochrome c oxidase, COX) activities were measured and normalized to activity of citrate synthase (CS) in the mitochondrial suspension. Values are shown as percent of the following absolute values in controls: NQR 0.30, NCR 0.80, SDH 0.32, SCR 0.51 and COX 2.29 units/unit CS. (D) The ATP production rate determined in isolated, intact mitochondria in the presence of substrates glutamate + succinate (G + S), glutamate + malate (G + M), TMPD + ascorbate (T + A), pyruvate + malate (P + M), palmitoyl-l-carnitine + malate (PC + M), succinate (S) and succinate + rotenone (S + R). Activities were normalized to CS activity in the mitochondrial suspension and shown as percent of the following absolute values in controls: G + S 0.19, G + M 0.14, T + A 0.15, P + M 0.11, PC + M 0.095, S + R 0.027 and S 0.023 units/unit CS. (E) CS and GDH activities in heart tissue. Activities were normalized to tissue mass and shown as percent of absolute values in controls: 347 mmol/min/kg for CS and 13.4 mmol/min/kg for GDH. (F) Immunoblots from total extracts of control (Ct) and Ndufs4 knockout (KO) hearts (age ∼12 months). Open bars, controls; black bars, Ndufs4 heart knockouts. Data shown as mean ± s.e.m. (n = 5). *P < 0.05; **P < 0.01; ***P < 0.001 by Student's two-tailed t-test following Levene's test for equality of variance.