THE NATURE OF BLOOD LIPIDS 361 



8.5% of phospholipids, 16.4% of cholesterol, and 20.4% of fatty acids. 

 Oncley et a/. 75 prepared two lipoproteins, by low temperature alcohol frac- 

 tionation of human plasma, which contained 35 and 75% of lipid; these 

 were shown to be related to cm- and ft-globulins. 



Oncley, Gurd, and Melin 76 separated a ft-globulin fraction from human 

 serum which contains 29% of phospholipid, as well as 39% of cholesterol 

 esters and 8% of free cholesterol. The nitrogenous portion of this con- 

 jugate protein accounts for only 23% of the total weight. 



(4) Cerebrosides 



The cerebrosides (galacto- or glucolipids) are another group of conju- 

 gate lipids present in the blood. Although the latter compounds do not 

 contain phosphate, they may be confused with the phospholipids (particu- 

 larly sphingomyelin), because of the high concentration of sphingosine in 

 their molecules. Moreover, the phospholipids and the cerebrosides both 

 have a wide distribution in animal tissues. 77 



Erickson and her collaborators 78 reported the presence of 15 milligram 

 per cent of cerebrosides in the serum, while Kirk 60 found an average figure 

 of 42 milligram per cent. However, in the later tests, the individual values 

 were extremely variable. These figures represent 2 and 8% of the total 

 plasma lipids, respectively. 



Cerebrosides have likewise been noted in leucocytes and pus cells, 79,80 as 

 well as in fish sperm. 81 Schonheimer 82 demonstrated their presence in 

 atherosclerosis of the aorta. Kirk 60 has given the average cerebroside con- 

 tent of red blood cells as 51 milligram per cent. In addition to cerebrosides, 

 Klenk and Lauenstein 83 identified an additional sugar-containing lipid in 

 human red blood cells which was similar in composition to the gangliosides 

 of the spleen. It differed from the latter compounds, however, by the ab- 

 sence of neuraminic acid. The distribution of cleavage products of this 

 glycolipid was as follows: fatty acids (mainly lignoceric), 29%; sphingo- 



75 J. L. Oncley, G. Scatchard, and A. Brown, /. Phys. & Colloid Chem., 51, 184-198 

 (1947). 



76 J. L. Oncley, F. R. N. Gurd, and M. Melin, /. Am. Chem. Soc, 72, 458-464 (1950). 



77 M. Kaucher, H. Galbraith, V. Button, and H. H. Williams, Arch. Biochem., 3, 203- 

 215 (1943). 



78 B. N. Erickson, H. J. Souders, M. L. Shepherd, D. M. Teague, and H. H. Williams, 

 Proc. Soc. Exptl. Biol. Med., 45, 153-156 (1940). 



79 A. Kossel and F. Freytag, Z. physiol. Chem., 17, 431-456 (1893). 



80 F. Hoppe-Seyler, Med.-Chem. Untersuch., 4, 486-501 (1871). 



81 M. Sano, J. Biochem. {Japan), 1, 1-16, 17-20 (1922). 



82 R. Schonheimer, Z. physiol. Chem., 177, 143-157 (1928). 



83 E. Klenk and K. Lauenstein, Z. physiol. Chem., 288, 220-228 (1951). 



