The mitochondrial inner membrane contains the machinery of oxidative phosphorylation. This membrane has invaginations called cristae which vary widely in shape between organisms and between tissues in the same organism. Electron microscopic tomography indicates that, despite this pleiomorphism, there is a common design feature, namely, the cristal membranes connect to each other and to the periphery of the inner membrane by tubular regions 30-40 nm in diameter. This finding has important implications for the internal diffusion of ions, metabolites and macromolecules within mitochondria.
In some types of mitochondria, the cristae exhibit periodicity.1 In the case of the amoeba Chaos carolinensis, detailed analysis and modeling of thin-section images of mitochondria in starved cells indicate that the highly curved cristae correspond to periodic cubic surfaces. We are undertaking electron microscopic tomographic and crystallographic approaches to more thoroughly characterize these membrane phases and, in particular, establish the continuity of the internal compartments which they define.