Fatty Acids of Beef Heart Sphingomyelin

Abstract

A CERAMIDE lactoside, synthesized to approximate to the structure of the tumour hapten cytolipin H¹, was reported² to have a melting point of 86° C, which appeared low for a cerebroside analogue. A 25-mg sample was absorbed on 7 g silicic acid : ‘Celite’ (5 : 2) in chloroform, and eluted with increasing methanol concentrations in chloroform. At 5 per cent methanol, about 2 mg of ceramide (m.p. 84°–86° C) was obtained, while the bulk of the material, recovered at 30 per cent methanol, had an infra-red spectrum identical to that of the original material, and a melting point of 167°–170° C (measured on a Kohfler micro-hot stage). Under the same conditions, authentic cytolipin H melted at 174°–183° C. At this point, it appeared that the original sample had contained about 10 per cent ceramide (by weight), a contaminant which could not be detected in the infra-red spectrum at that concentration. But the differences in the new melting points could be accounted for by differences in the fatty acids residues of both compounds. A preliminary attempt at the identification of the fatty acid residues of the ceramide lactoside indicated that lignoceric acid (C₂₄, tetracosanoic acid) made up only one-third of the total fatty acids residues, while another one-third was made up on some odd-number saturated fatty acid. It was, therefore, of interest to determine the components of the fatty acid mixture in the sphingomyelin from which the ceramide was prepared for the synthesis of ceramide lactoside.