Effect of serum on the isolated CNS myelin membrane

Rabbit brain myelin was incubated with rabbit serum, and changes in protein components were measured following re-isolation of the membrane by ultracentrifugation. Basic protein was substantially degraded by proteolytic enzymes present in serum. No breakdown of other major myelin proteins was observed. Some serum proteins became firmly associated with the myelin membrane during the incubation. Furthermore, the incubation of myelin with serum resulted in formation of denser myelin particles, which sedimented in 0.625 M sucrose. This process appears not to be related to the removal of basic protein from the membrane. The basic protein-digesting activity of human serum was comparable to that of rabbit serum, and no difference in the activity between sera from multiple sclerosis and control patients was observed. The possible relevance of these findings to demyelinating diseases is discussed.