The chemical nature of the fatty acids of brain and spleen sphingomyelin; the occurrence of saturated and unsaturated sphingosines in the sphingomyelin molecule.

Sphingomyelin prepared with the older methods from brain and spleen yielded on acid hydrolysis palmitic, stearic, and lignoceric acids (1, 2). Mere found that in addition to these saturated acids nervonic acid is present in the sphingomyelin of brain (3). The presence of palmitic acid in the sphingomyelin molecule of brain seemed questionable, since it was shown that sphingomyelin prepared by the usual method is a mixture of hydrolecithin (dipalmityl lecithin) and sphingomyelin. It is the purpose of this paper to describe a procedure for the preparation of sphingomyelin free of hydrolecithin from brain and spleen, and to reinvestigate its component fatty acids. In pure sphingomyelin of brain, stearic acid, lignoceric acid, and its unsaturated compound, nervonic acid, are present. No palmitic acid was found. Stearic acid and nervonic acid are present in larger quantities than is lignoceric acid. Sphingomyelin free of hydrolecithin was prepared from spleen according to the method previously described for the isolation of pure sphingomyelin from lung (4). The fatty acids present in the sphingomgelin of spleen are the same as those found in sphingomyelin of lung; namely, palmitic acid and lignoceric acid in about equal amounts. Carter and coworkers (5, 6) have shown that sphingosine present in the cerebroside molecule is partly saturated (hydrosphingosine) and partly unsaturated sphingosine. The findings of Carter prompted us to isolate sphingosine after acid hydrolysis of sphingomyelin and to investigate whether or not saturated sphingosine is, as in cerebrosides, also a constituent of the sphingomyelin molecule. Crystalline sphingosine sulfate was isolated from pure sphingomyelin of brain and spleen. In both types of sphingomyelins the isolated sphingosine sulfates had iodine numbers which were much lower than that calculated for unsaturated sphingosine sulfate. It seems therefore justified to assume