Resin development for electron microscopy and an analysis of embedding at low temperature*

SUMMARY We have tested a wide range of acrylate and methacrylate resin formulations and have concluded that embedding resins can be developed which are usable within a broad range of environmental conditions. To demonstrate this versatility, we have designed two highly‐cross‐linked resins, one polar and the other nonpolar, that are usable to temperatures from 243 to 223 K. Both of these resins formulations, which are now commercially available, show that systematic experiments can be easily done to study the effects of environmental parameters, such as water content, temperature, or resin polarity, on biological material during embedding. Using these resins and aldehyde‐fixed protein crystals, it can be shown that low temperature minimizes the loss of molecular structure to an extent that is not often obtainable with conventional methods of dehydration and embedding. Embedded crystals of aspartate aminotransferase still retained molecular order to 0·6 nm. Embedded crystals of catalase show X‐ray diffraction maxima out to 0·8 nm. When sectioned, catalase revealed stain‐limited electron and optical diffraction patterns to 2·5 nm. Nevertheless, our work clearly demonstrates that low temperature embedding procedures are superior and that versatile, general purpose resins can be designed to take advantage of this fact.