354 V. BLOOD LIPIDS 



in combination with cholesterol, as the cholesterol ester fraction. As has 

 been noted above, the iodine numbers of the fatty acids in the cholesterol 

 fractions were 145 and 130 in cows, 16 and 158 in human plasma. 17 Channon 

 and Collinson 20 demonstrated that arachidonic and linoleic acids occur in 

 the acetone-soluble fraction of beef blood, along with palmitic and stearic 

 acids. Kelsey and Longenecker 22 reported 62% of linoleic acid in choles- 

 terol esters of the acetone-soluble fraction of cow plasma, as contrasted 

 with only 18% of this dienoic acid in the glyceride fatty acids These 

 figures correspond to values of 55 and 25%, respectively, found by Channon 

 and Collinson. 20 In sharp contradistinction to these results, Keegan and 

 Gould 23 isolated cholesteryl oleate from dog and human plasma; it is diffi- 

 cult to explain how cholesteryl oleate could be present in sufficient amounts 

 to be isolated, in view of the prevailing iodine numbers previously reported 

 for the cholesteryl esters. The results of Kelsey and Longenecker 22 are 

 summarized in Table 1 on page 353. 



c. Fatty Acids Combined with Protein. It is now believed that the 

 plasma fatty acid fraction, which was formerly classed as free fatty acids, 

 actually represents a fraction combined with protein. The first evidence 

 of a protein-fatty acid combination was given by Macheboeuf and Tayeau. 24 

 Almost simultaneously, Kendall 25 prepared a crystalline serum albumin 

 from human serum which contained 2% of a fatty acid ; this could be freed 

 from the protein only by denaturation of the lipoprotein molecule. 



Indirect evidence cited by Luck, 8 which confirms the protein-fatty acid 

 association, includes that obtained from dialysis-equilibrium studies, as 

 demonstrated by effects on absorption spectra, and by binding studies on 

 dyes, on indicators, and on synthetic detergents. Scatchard and Black 26 

 have shown that serum albumin solutions, which have been rendered iso- 

 ionic by exhaustive dialysis against water, exhibit a decrease in pH. of as 

 much as 1.65 pR units when various neutral inorganic salts are added. 

 These results are interpreted to mean that an anionic binding of the fatty 

 acids has been disrupted by this procedure. The results of Longsworth 

 and Jacobsen 27 and of Velick 28 afford similar evidence. The dialysis- 

 equilibrium method was first introduced as a tool by von Muralt 29 in 1930; 



22 F. E. Kelsey and H. E. Longenecker, J. Biol. Chem., 129, 727-740 (1941). 



23 P. Keegan and R. G. Gould, Federation Proc, 12, 228-229 (1953). 



24 M. A. Macheboeuf and F. Tayeau, Bull. soc. chim. biol, 23, 49-61 (1941). 

 26 F. E. Kendall, J. Biol. Chem., 138, 97-109 (1941). 



26 G. Scatchard and E. S. Black, /. Phys. & Colloid Chem., 53, 88-99 (1949). 



27 L. G. Longsworth and C. F. Jacobsen, J. Phys. & Colloid Chem., 53. 126-135 (1949). 



28 S. F. Velick, /. Phys. & Colloid Chem., 58, 135-149 (1949). 



29 A. L. von Muralt, J. Am. Chem. Soc, 52, 3518-3523 (1930). 



