A preparation of proteolipid, the principal component of the myelin sheath, was obtained from the bovine brain white matter with satisfactory reproducibility. Much of the lipid portion, containing most of the component sphingomyelin, was removed by precipitation with a mixture of ethanol and ether, and the precipitate fraction exhibited a preferential affinity for sphingomyelin. Since phosphatidylcholine, which did not show so much combining affinity for the precipitate fraction, exhibited an enhanced interaction by means of hydrogenation of the fatty chains, it is assumed that the affinity of sphingomyelin depends on the hydrophobic region of the molecule. Sphingomyelin is considered to interact with a complex formed by the ionic linkage between the basic protein and acidic phospholipid, which is obtained by further removal of the lipid portion from the precipitate fraction by dialysis
