Complementary freeze-fracture and freeze-etch preparations

Abstract

Whereas freeze-etching technology was introduced in 1957 (1) and the first freeze-etching equipment to be made available commercially was developed in 1961 (2), the need for complementary replicas was not recognized until Branton (3) proposed that the two membrane faces seen in freeze-etched specimens were not the inner and outer surfaces of membranes but represented two new faces which resulted from the splitting of membranes between the two lipid layers. Several indirect methods were developed to test Branton's hypothesis and most of them provided confirming evidence. It became obvious that complementary replicas could provide the indisputable answer to this theory; wherever one membrane fracture face appeared on one specimen the other fracture face should appear in the same position on the complementary specimen. Several devices were developed to make possible the preparation of complementary replicas (4, 5, 6, 7).