title: Chemical aspects of glycogen contrast-staining by potassium osmate.
abstract: To obtain contrast-staining of glycogen in electron microscopy, various contrast-enhancing additives can be used in combination with potassium osmate. Examples are potassium ferrocyanide and certain nitrogen heterocyclic compounds, such as triazoles. In the reaction sequence leading to contrast-stained glycogen, a primary reaction is the formation of glycogen osmate. This reaction was studied with isolated glycogen. On the basis of the stoichiometric findings, a molecular structure of the reaction product is proposed; apparently, osmate is bound by glycogen because of the presence of suitably located hydroxyl groups. The resulting compound is not itself sufficiently electron dense, but it binds 1,2,4-triazole as an additional ligand. Secondary reactions can result in additional osmium binding, and finally to osmium (IV) deposits, leading to contrast.
mesh_terms: D006003:Glycogen / Q000032:analysis*; D008854:Microscopy, Electron; D009992:Osmium; D009993:Osmium Tetroxide; D011188:Potassium; D013057:Spectrum Analysis; D013194:Staining and Labeling; D014230:Triazoles
chemical_list: D014230:Triazoles; D009992:Osmium; D006003:Glycogen; D009993:Osmium Tetroxide; D011188:Potassium