THE NATURE OF BLOOD LIPIDS 371 



Lepeschkin, 146 and Marrack, 146 as well as in several papers by Chargaff and 

 associates. 147-160 Information on lipoproteins is contained in the Dis- 

 cussions of the Faraday Society, 151 which records results of a conference on 

 lipoproteins held in Birmingham, England, in August, 1949. Much of the 

 work reported in the above monograph concerns the lipoprotein compo- 

 nents of the blood. 



The lipoproteins are widely distributed in living matter, where they occur 

 in cell nuclei, mitochondria, cell membranes, chloroplasts, in egg yolk, in 

 milk, and in blood. Chargaff reported the separation of a thromboplastie 

 protein of this type from the lungs 149 ; the nature of lipovitellin from egg 

 yolk and of mitochondria lipoproteins has also been described. 152 



A phase of prime importance in the present discussion is the nature of the 

 lipoproteins in blood. In the previous sections, it was pointed out that 

 neutral fats, fatty acids, lecithins and other phospholipids, cholesterol, 

 carotenoids, and vitamin A are combined with plasma proteins. The 

 nature of the protein moiety of the plasma lipoproteins will be considered 

 in more detail in the present section. 



Until the classical studies of the Cohn group at Harvard, which involved 

 a large-scale fractionation of human plasma at low ionic strength, by the 

 use of ethanol-water mixtures at low temperatures, 153 it was believed that 

 the blood lipids were present in solution in the blood. It was therefore 

 expected that the lipids would remain in the residual ethanol-water mixture 

 from which the proteins had been precipitated. However, such was not 

 found to be the case. The blood lipids were identified in two distinctly 

 different types of lipoproteins, which were present in readily separable pro- 

 tein fractions. 



Further evidence of the nature of lipoproteins has been obtained by 

 Turner et al. 15i through the use of centrifugation. About one-half of the 



146 yy. W. Lepeschkin, Kolloidchemie des Protoplasmas, Steinkopff, Dresden-Leipzig, 

 1938, p. 155 ff. 



146 J. R. Marrack, The Chemistry of Antigens and Antibodies, Med. Research Council, 

 Special report Ser. No. 194, London, 1934. 



147 E. Chargaff, /. Biol. Chem., 125, 661-670 (1938). 



148 E. Chargaff and M. Ziff, J. Biol. Chem., 131, 25-34 (1939). 



149 S. S. Cohen and E. Chargaff, /. Biol. Chem., 136, 243-256 (1940). 



160 S. S. Cohen and E. Chargaff, /. Biol. Chem., 139, 741-752 (1941). 



161 General Discussion Faraday Soc, No. 8, Lipoproteins, 5-167, Aberdeen Univ. 

 Press, Aberdeen, 1949. 



152 E. Chargaff, J. Biol. Chem., 142, 491-504 (1942). 



153 J. T. Edsall, "The Plasma Proteins and Their Fractionation," Advances in Protein 

 Chem., 3, 383-479 (1947). 



164 R. H. Turner, J. R. Snavely, W. H. Goldwater, M. L. Randolph, C. C. Sprague, 

 and W. G. Unglaub, /. Clin. Invest., 30, 1071-1081 (1951). 



