Extraction of proteins and membrane lipids during low temperature embedding of biological material for electron microscopy.

The extraction of proteins and membrane lipids from biological materials during embedding procedures for electron microscopy carried out at temperatures down to 223 K was studied. Glutaraldehyde-fixed cells of Acholeplasma laidlawii mainly served as test material. More than 99% of the protein and 88% of the lipid of these cells were retained after dehydration with ethanol or acetone between 277 and 223 K and infiltration with methacrylate at 223 K. When methanol was used for dehydration, only 54% of the lipid was retained. The amount of extracted lipid was essentially independent of the ratio between volume of extraction liquid and amount of material subjected to extraction. The cytoplasmic membrane of sectioned Acholeplasma-cells dehydrated and infiltrated as described above appeared more diffuse than that of cells fixed with glutaraldehyde and osmium tetroxide in epoxy resin at room temperature. Glutaraldehyde-fixed erythrocyte ghosts retained 85% of their phospholipid content when dehydrated with ethanol between 277 and 223 K and infiltrated with methacrylate at 223 K. Spinach chloroplasts and thylakoid vesicles retained 61% and 35%, respectively, of their chlorophyll content.