""""""""Label-fracture"""""""" allows the observation of cytochemical label on the cell surace. Cell surfaces labeled with colloidal gold are freeze-fractured and the fracture faces are replicated by Pt/C. The exoplasmic halves of the membrane are washed in distilled water. The new method reveals the surface distribution of the label coincident with the Pt/C replica of the exoplasmic fracture face. Initial applications indicate exceedingly high resolution (less than 5 nm) and low background. """"""""Label-fracture"""""""" views of the distribution of the label on membrane surfaces while preserving cell shape and relating to the freeze-fracture morphology. Label-fracture is appropriate for routine use as a surface labeling technique. Mapping of WGA and Con A receptors on the cell surface of boar sperm reveals intense WGA surface labeling over the region of the plasma membrane that overlies the acrosome. High density of WGA receptors is revealed over particle-free zone located at the base of the head. The density of WGA receptors in the tail is high over the mid-piece, annulus and principal piece. Intense labeling by Con A is observed over the sperm head with the exception of the particle-free zone at the base of the head where Con A receptors are absent. In the tail, Con A labeling is strong over the mid-piece, absent over the annulus and sparse over the principal piece. In contrast to WGA, Con A receptors appear to codistribute with the intermembrane particles. Our results confirm the exceptional prmoise of """"""""label-fracture"""""""" to establish the surface distribution of antigents and receptors. Other label-fracture studies are underway: (1) apical surfaces of toad bladder epithelial cells; (2) localization and capping of cholera toxin receptors; (3) differences related to all aging and translocation; (4) capping of surface IgG in lymphocytes; (5) localization of insulin receptors on adipocytes.
