[Electron microscopic study of the chemical structural asymmetry of myelin sheaths]

Osmium washing of ultrathin sections of the frog sciatic nerve myelin fibres performed with 4% acetic acid solution preceded their treatment with the Dragendorf solution and ammonium paramolibdate. This enabled us to localize amine and phosphate groups of myelin membranes. The data obtained suggest that the majority of phospholipids of these membranes are located on the cytoplasmic surfaces, whereas glycolipids and cholesterol--on the extracellular ones. Examination of these surfaces by freeze--fracturing revealed different hydratation degrees in these surfaces. These results show that myelin membranes are most convenient models for the study of structural and chemical asymmetry of biological membranes.