Electron Microscopical Study of Intramembranous Changes in 
Protein-extracted Peripheral Nervous System Myelin

While the freeze-fracture technique is able to visualize macromolecules, without some identification as to which intramembranous particles represent specific proteins, it is difficult to correlate specific biochemical changes with specific regional changes in membrane.  A carefully controlled extraction technique using Triton X-100 selectively removes one group of proteins (the myelin basic proteins, or MBPs) from the myelin sheath.  Myelin sheaths treated to selectively remove MBPs were examined using freeze-fracture.

The results indicated that extraction of MBPs causes a separation of the myelin lamellae along the major dense line and produces areas of intramembranous particle loss in freeze-fracture replicas.  Chemical fixation for as short a time as 15 minutes was sufficient to prevent the particle rearrangements, indicating that normal chemical fixation procedures stabilize the membrane and give an image similar to the in situ arrangement of components.  The extensive alteration of the sheath by the extraction procedure made it difficult to assess whether a specific intramembranous particle size or shape could be correlated with the MBPs.