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DETECTION OF MYELIN IN THE OPTIC NERVE OF YOUNG RATS BY SEDIMENTATION EQUILIBRIUM IN A CsCl GRADIENT 1

—A method is described for detecting myelin in small amounts of tissue by density criteria. Samples are homogenized in 0.926 m‐CsCl, 10 mm‐Tris‐HCl, (pH 7.4), 5 mm‐Ca2+ solution and centrifuged to equilibrium at 52,000 rev./min and 4°C in the AN‐F rotor of the Model E analytical ultracentrifuge. Homogenates of white matter show a band of material in the density range of 1.20–1.130 g/ml, whereas gray matter homogenates do not show a band of material in this density region. A preparative method is described for isolating the material banding in the region of 1.120–1.130 g/ml from optic nerve homogenates of 21‐day old rats. This material has (1) a protein content of 22–24%, (2) an enzymatic activity for 2′,3′‐cyclic nucleotide phosphohydrolase of 13.1 μmol/min per mg protein and (3) a phospholipid‐cholesterol‐galactolipid molar ratio of 100:100:48. Plasmalogen accounted for 22% of the phospholipid, and sulfatide accounted for 31% of the galactolipid. This material is 85% soluble in chloroform:methanol (2:1. v:v). Developmental studies indicate that this myelin material can first be detected in the optic nerve from an 11‐day‐old rat.