THE NATURE OF BLOOD LIPIDS 365 



occurs. In some instances, a new lipoprotein, having a lower density and 

 containing cholesterol, was obtained; this had an Sf of 10 to 30. There 

 appeared to be some correlation between the appearance of this second lipo- 

 protein and the onset of mild to severe atherosclerosis. 96 



In some samples of human sera, a second component of the lipoprotein 

 occurred, similar to that reported for rabbit blood. The human lipo- 

 protein was also characterized by the S f value of 10 to 20. It was found 

 that, in a study of 104 patients who had previously experienced myocardial 

 infarctions, the appearance of the new lipoprotein fraction was almost 

 universal. The Sf 10 to 20 fraction occurred less frequently in measurable 

 concentrations, in healthy subjects, than in those who had experienced cir- 

 culatory disturbances. It is believed that the level of the Sf 10 to 20 frac- 

 tion may afford an index of the susceptibility of an individual to athero- 

 sclerosis. A further discussion of these results has been given by Gofman 

 etaU 8 



b. Hydrocarbons. Although hydrocarbons form an extremely minor 

 proportion of the unsaponifiable fraction, a number of paraffins and higher 

 alcohols which have been shown to occur in the body tissues undoubtedly 

 are carried in the blood. However, in the studies of Setala and Ermala" 

 on the carcinogenic hydrocarbon, 3,4-benzpyrene, it was found that this 

 substance or its metabolites exist in the blood in association with chylo- 

 microns after the hydrocarbon, dissolved in fats, has been absorbed from 

 the intestines. 



c. Carotenoids. /3-Carotene may be present in the blood of animals 

 in which the main site of conversion to vitamin A is the liver rather than 

 the intestinal wall. Thus, the presence of carotene has been noted in 

 human blood serum 100,101 and in that of cattle. 102-105 Mehl 106 first observed 

 that nearly all the carotenoid of human plasma is to be found associated 

 with a /3-lipoprotein. This result has been confirmed and extended in a 

 recent communication by Ganguly et al., 6 in which it is proved that the 



98 J. \V. Gofman, H. B. Jones, F. T. Lindgren, T. P. Lyon, H. A. Elliott, and B. Stri- 

 sower, Circulation, 2, 161-178 (1950). 



99 K. Setala and P. Ermala, Science, 114, 151-152 (1951). 



100 T. Willstaedt, and T. Lindqvist, Z. physiol Chem., 240, 10-18 (1936). 



101 H. Willstaedt and T. K. With, Z. physiol. Chem., 253, 40-46 (1938). 



102 B. v. Euler, H. v. Euler, and H. Hellstrom, Biochem. Z., 208, 370-384 (1928). 



103 L. S. Palmer and C. H. Eckles, /. Biol. Chem., 17, 223-236 (1914). 



104 L. S. Palmer, Carolinoids and Related Pigments, Chem. Pub. Co., New York, 1922, 

 p. 208. 



105 J. Ganguly, J. W. Mehl, and H. J. Deuel, Jr., J. Nutrition, 50, 73-84 (1953). 



106 J. W. Mehl, Personal communication, 1944; also cited by F. R. N. Gurd, J. L. 

 Oncley, J. T. Edsall, and E. J. Cohn, in Lipoproteins, General discussion Faraday Soc, 

 No. 6, 70-74, Aberdeen Univ. Press, Aberdeen, 1949, p. 73. 



