Figure 1. Fatty acid uncoupling efficiency in brown-fat mitochondria and liver from wild-type and UCP1^−/− mice.

Representative traces showing the effects of oleate (solid line) and FCCP (broken line) on respiration of liver mitohondria from UCP1^−/− mice (a) and brown-fat mitochondria from UCP1^−/− (b) and wild-type (c) mice. Pyr, addition of 5 mM pyruvate; GDP, addition of 1 mM GDP. FCCP and oleate were successively added to the concentrations indicated. (d) Dose–response curve for FCCP compiled from experiments as in (a– c). Values are means±S.E.M. from five to seven independent mitochondrial preparations. Curves were drawn for simple Michaelis–Menten kinetics. (e and f) Oleate concentration–response curves for brown-fat (solid line) and liver (broken line) mitochondria from wild-type and UCP1^−/− mice. The experiments were performed principally as those illustrated in (a– c). The brown-fat data set in (d– f) includes a few also included in [14]; however, all brown-fat experiments presented here (but not all in [14]) had been performed in parallel with liver preparations. In (f), the change in oxygen consumption (Δ nmol of O₂·min⁻¹·mg of protein⁻¹) from the coupled state (in the presence of 1 mM GDP) is shown. The points are means±S.E.M. for seven to nine independent mitochondrial isolations for each group. The x-axis indicates the free oleate concentrations calculated as described in the Experimental section. Curves were drawn for simple Michaelis–Menten kinetics. For ΔV_max and K_m calculations, concentration–response curves were individually analysed in each mitochondrial preparation. These results are shown in Table 1.