Freeze-etching electron microscopy of serum lipoproteins

The structure of serum lipoproteins in solution has been investigated by freeze-etching electron microscopy employing rapid freezing techniques. Turnip yellow mosaic virus was used to demonstrate the performance of these techniques and their capability to provide information about the structure of particles in solution. Low-density lipoproteins appeared to deviate markedly from a smooth spherical shape. Instead, the outer layer of the particles appeared to consist of a small number of globules. The number, dimensions, and arrangements of the globules agree remarkably with the tetrahedral model proposed by Luzzati et al. for the low temperature form of LDL. Further, we show that the freeze-etching electron microscopy technique may be capable of providing structural information with other lipoproteins.