Isolated mouse liver mitochondrion treated with wild type tBid and labeled with 10 nm immunogold particles. a) Electron micrographs of thin sections (~50 nm thick) were examined to ascertain the quality of ultrastructural preservation and immunogold labeling density. On occasion, contact sites were observed; in these situations, a gold particle appeared to be nearby. For the most part, mitochondria treated with this tBid displayed rather poor preservation of the outer membrane, which may be a reflection of the activity of this pro-apoptotic protein in causing cytochrome c release. Neither was the gold labeling very high, most likely because a stripped outer membrane represents considerably fewer contact sites.b) One slice through a tomographic reconstruction showing partial stripping of the outer membrane. Largely, WT tBid was observed to be in close proximity to contact sites. Examples are indicated by arrows (gold particle) and arrowheads (contact site). Yellow traces indicate regions around the periphery where the outer membrane was stripped away. This mitochondrion is more in the orthodox state  than most observed. Horizontal streaks were caused by reconstructing the electron-dense gold particles and sometimes obscure features (bottom of image). Scale bars: (a), (b), 300 nm.
Lutter et al. BMC Cell Biology 2001 2:22 doi:10.1186/1471-2121-2-22