Electron Microscopy of Negatively Stained and Unstained Fibrinogen

Electron microscopic images of negatively stained fibrinogen are predominantly asymmetric rods 450 angstrom in length and about 60 angstrom in width. The molecules appear to have considerable flexibility, and mass distribution along the major axis is not uniquely distinguished despite apparent beading in some particles. Scanning transmission electron microscopy of unstained fibrinogen again demonstrates that a majority of molecules are rodlike. The results differ from those obtained by negative staining in that a substantial fraction of images are trinodular with striking resemblance to those obtained by C. E. Hall and H. S. Slayter [J. Biophys. Biochem. Cytol. (1959) 5, 11-16] using the mica replica technique. The above results were obtained on glow-discharged carbon substrate films by a simple low-concentration, long-attachment-time modification of standard deposition methods that is diffusion controlled and depends on concentration and time but is independent of pH, buffer, and other staining conditions. Evidence is presented that standard attachment procedures result in artifactual images. Any model of fibrinogen in solution consequently must encompass properties that permit its visualization as an asymmetric rod by electron microscopy as first suggested by Hall and Slayter 20 years ago.