Fig. 4. Electron microscopy of 2-dimensional crystals of VDAC channels induced in the outer membranes of N. crassa mitochondria by slow phospholipase treatment. Both figures have been computer filtered and averaged with respect to the 6-channel repeating unit. The upper panel shows a surface view obtained by freeze-drying and shadowing these crystals (courtesy of Lorie Thomas). The openings of the channels are seen as dark depressions. The lower figure shows the crystals after freezing in a thin layer of vitreous ice (courtesy of Carmen Mannella). The white areas are the channel lumens and the dark areas are the protein structures. The circle indicates the center of a location surrounded by 6 channels. This location corresponds to the elevated (white) region in the upper panel.