Changes in freeze-fractured mitochondrial membranes correlated to their energetic state. Dynamic interactions of the boundary membranes.

Structural changes of mitochondria in correlation to their energetic state have been observed as matrix expansion and condensation. In this communication we describe a morphological correlation in freeze-fractured mitochondrial membranes which is also dependent on the metabolic state of the organelle: the frequency by which the fracture plane following the inner or outer boundary membrane deviates by jumping from one membrane to the other is higher in phosphorylating mitochondria when compared to freshly isolated or energized mitochondria. These deflections of the fracture plane occur mostly in minimal, short steps showing close apposition of the two boundary membranes. We therefore conclude that the observed change in morphological appearance is produced by a change in interactions between the inner and outer membranes correlated to the different functional states of the inner membrane.