Identification of phosphatidal choline as the major constituent of beef heart lecithin.

In the course of a study of the analytical determination of ester groupings in naturally occurring phospholipides, we found that a specimen of beef heart lecithin, prepared according to the method of Pangborn (l), regularly gave ester values considerably below those obtained with egg lecithin. The preparation was presumably pure, since it was colorless, free of amino nitrogen, had a molar N:P ratio of 1, and was satisfactory for serological analysis by stringent requirements (2). We were at the time primarily concerned with the chromatographic isolation of the naturally occurring plasmalogens from beef muscle (3) and were thus led to examine the preparation by a quantitative modification of the Schiff test for aldehyde-containing phospholipides. The rather startling result was that the specimen of beef heart lecithin was as chromogenic as any we had obtained by chromatographic separation, and the color yield was considerably in excess of that of a specimen of crystalline brain acetal phospholipide isolated by Thannhauser, Boncoddo, and Schmidt (4). Since the reliability of the Schiff test as a measure of aldehyde content in the presence of unsaturated structures is somewhat doubtful (5), an independent method of confirmation of aldehyde content was required. We therefore applied the quantitative method of Korey and Wittenberg (6), based on p-nitrophenylhydrazone formation, which showed that the aldehyde content was approximately the same as that of crystalline brain acetal phospholipide and equal to at least 0.5 mole of aldehyde per atom of phosphorus. We have now determined the aldehyde content of nine different beef heart lecithin preparations both by this method and the Schiff reaction. The uniformity of results establishes t,he presence of a cholinecontaining plasmalogen as the major constituent. of beef heart lecithin. In view of the very close relationship of the naturally occurring aldehydecontaining phospholipides to phosphatidyl choline and phosphatidyl ethanolamine, we propose to call them phosphatidal choline and phosphatidal ethanolamine.