Electron microscopy : use of lectin-gold after embedding

Fixation of tissues for postembedding gold-lectin histochemistry calls for a fixative that preserves the ultrastructure of the tissue, has no inhibiting effect on lectin binding sites, and binds the glycoconjugates, which carry these lectin binding sites within the tissue so strongly that they cannot be washed out during the dehydration and ensuing embedding steps. There is no "one and only" fixative that has all these properties, and every fixative used for postembedding gold-lectin histochemistry must be viewed, at best, as a compromise. One common fixative, more or less exhibiting the properties required, is a mixture of 4% formaldehyde and 0.5% glutaraldehyde in phosphate buffer at pH 7 35. The use of osmium tetroxide as a fixative must, in general, be avoided for postembedding lectin histochemistry since it disturbs the reactivity of lectin binding sites.