Membranes: Freeze-etching techniques applied to biological membranes

Abstract

Basic freeze-etching methods are described. When biological membranes are freeze-fractured the fracture plane is smooth, but interrupted to a greater or lesser extent by numbers of small (8.5 nm) particles. The evidence that the fracture occurs in the interior of the membrane and that the particles represent proteins within the membrane is reviewed. A problem of interpretation of freeze-fracture replicas is that the two 'complementary’ faces, produced by the fracture of a single membrane, do not match exactly. In particular, particles on one face are often not matched by corresponding depressions on the other. Work in the author’s laboratory using the complementary replica technique is described. One conclusion from this work is that plastic deformation of the intra-membrane protein particles may occur, and that this may be responsible for the lack of small-scale complementarity.