The Lecithin, Cephalin, and Sphingomxelin Content of Serum* I. as Indicated by the Choline-phosphorus and Nitrogen-phosphorus Ratios by R. G. Sinclair with the Assistance of Henry Tsuyuki and Eve Minovitch

In 1944 Taurog, Entenman, and Chaikoff (13) reported that the ratio of choline to phosphorus in the acetone-insoluble lipides of human and dog plasma was close enough to 1.0 to justify the conclusion that cephalin was almost, if not entirely, absent. Although instances of the absence of cephalin from plasma had been reported before (1, 8, 14), most of the earlier work (cited in (13)) had indicated that some 20 to 40 per cent of the plasma phospholipides consisted of cephalins, or at least of non-cholinecontaining phospholipide. In spite of the wealth and consistency of the data presented by Taurog et al. (13) and later by Entemnan and Chaikoff (3), a further and independent study of the problem seemed desirable. This was the primary object of the present work. However, the study was extended to the serum ‘of beef, pig, and turkey, as well as to human and dog sera. Furthermore, the experiment was so planned as to obtain information on the sphingomyelin and lecithin, as well as on the cephalin, content of the various sera. It so happened that at the same time Hack (9) had undertaken a somewhat, similar study of the composition of human plasma phospholipides. His data show that in the fasting human subject the plasma phospholipides, on the average, consist of 79 per cent lecithin, 16 per cent sphingomyelin, and 5 per cent cephalm. In the individual subjects, however, cephalin was found to vary from 0 to 17 per cent of the total. The general plan of the present work was to isolate the lipides from relatively large volumes of serum or plasma, to fractionate them into acetone-soluble and acetone-insoluble fractions, and to purify the latter in such a way as to insure that it contained only lipide nitrogen, phosphorus, and choline. Dialysis was chosen as the most satisfactory method of removing non-lipide impurities. The choline to phosphorus (C: P) ratio