Myelin basic protein and the stability of the multilamellar myelin structure.

A purified myelin fraction was prepared from myelin deficient (mld) mutant mice and normal littermates (20 to 25 days old). Mld brains contained only 5% of the amount of myelin present in controls. Myelin isolated from mld brains had a normal lipid and protein content. The lipid composition of mld myelin was also normal. Myelin basic protein (MBP) was nearly missing in mld myelin. At the electron microscope, in mld myelin, the major dense line was often missing and the myelin lamellae were uncompacted. The high specific radioactivity of the myelin associated glycoprotein and sulfatides, two myelin constituents which are not affected by the mutation, indicate a high turnover rate of myelin membranes in the mld mutant. Furthermore, the presence of increased amounts of cholesterol esters in mld brains suggests that myelin in mld mutants is unstable. We propose that MBP, which is responsible in the central nervous system for myelin compaction, is responsible for the stability of this membrane.