Fig. 2. The dependence of tBid-induced cytochrome c release on mitochondrial concentration. (Top) tBid (15 nM)-induced cytochrome c release was measured with either 4, 8, 15 or 31 µg of mitochondrial protein per reaction volume (20 µl), as indicated. Arrows show the [tBid] giving half-maximal cytochrome c release (EC50 values). (Bottom) The EC50 values are plotted against mitochondrial protein per reaction.