Some observations on negatively stained mitochondria.

A particulate component of mitochondria is described which is observed in negatively stained preparations of unfixed whole mitochondria or their fragments. It consists of a roughly spherical particle, approximately 85 A in diameter, found on the surface of the cristae and probably also on the side of the mitochondrial envelope which faces the matrix. It is attached to the underlying membrane by a narrow stalk 40 to 50 A long. The particle appears to be rather labile and it is destroyed or at least rendered unrecognizable by all conventional fixatives used in electron microscopy, especially OsO(4).