Complementary structures of membrane fracture faces obtained by ultrahigh vacuum freeze-fracturing at -196 degrees C and digital image processing

Abstract

Conventional freeze-etch replicas of the cytoplasmic fracture face (PF) of the yeast plasmalemma membrane show hexagonally ordered regions. Complementary features on the extraplasmic face (EF) could not be identified. Replicas with improved topographical resolution were obtained for both fracture faces by ultrahigh vacuum freeze-fracturing at -196 degrees C. The hexagonally ordered structure on the PF is seen to consist of volcano-like particles with a crater of 5 nm diameter. The lattice constant is 16.5 nm. On the EF, ring-like depressions corresponding to particles on the PF can occasionally be detected; the existence of ordered regions can be established by optical diffraction. Complementarity of periodic features on the PF and EF is demonstrated by digital image filtration. A main structure, coarse features of which appear on conventional PF replicas is shown to have perfect complementarity at a resolution level of 2 nm. On the EF an additional substructure, completely obscured on normal replicas, is revealed. Its complementarity remains tentative as shadows cast by the main structure impair identification of substructural features on the PF.