A high-resolution membrane probe
Labeling the lipids of membranes for E.M. is frequently done by using radioactive phospholipids. Membrane dynamics can then be followed by autoradiography. Unfortunately, it takes approximately 6 months to expose the emulsion due to the low specific activity of the labels. Also, the resolution is limited to about 0.2 μm by this technique.An alternative is to develop a phospholipid-like molecule that is electron dense and could be visualized directly. Several such molecules have been synthesized and one is shown in Fig. 1. They have a phosphotungstate “head” group that has a 4 (-) charge and is hydrophilic and an aliphatic “tail” of varying length that is hydrophobic. The tungstate cluster contains 11 tungsten atoms in the “Keggin” structure with a 1.0 nm diameter and has previously been studied in the electron microscope. It was shown to be almost completely resistant to beam induced mass loss.