370 V. BLOOD LIPIDS 



the bulk of the blood tocopherol is the a-isomer 137 ; about 75% of the total 

 tocopherol consists of the latter compound, while other isomers comprise 

 the remaining one-quarter of the blood tocopherols. The vitamin occurs 

 as the free vitamin, even after a tocopherol ester has been adminis- 

 tered. 138 - 139 



The tocopherols are only slowly extractable from the plasma by hydro- 

 carbon solvents or by ether, and previous or simultaneous addition of 

 ethanol is required for satisfactory extraction. 140 For this reason, Hick- 

 man 141,142 suggested that tocopherol must occur in plasma in combination 

 with a plasma protein. Ames and Risley 140 demonstrated that blood 

 plasma is able to solubilize relatively large amounts of the tocopherols 

 (200-300 milligram per cent). On fractionation of the plasma proteins 

 with ammonium sulfate or ethanol, at low temperatures, a-tocopherol was 

 found in all resulting protein fractions. Amino acids or partially hydro- 

 lyzed proteins were not capable of bringing about a solution of tocopherol. 

 Since some of the proteins effective in facilitating the solution of a-toco- 

 pherol were lipid-free, it is suggested that the tocopherol-protein complex 

 may be entirely independent of any lipoprotein. 



(d) Vitamins K. Although there is every reason to suppose that vita- 

 min K is present in the blood of most animals, including that of man, data 

 are not at present available as to the amount of this vitamin or the type 

 which is present in blood. 



(7) Lipoproteins in the Blood 



Although it has been recognized for many years that protein-fat combina- 

 tions exist in nature, there had been but little advance in our knowledge 

 of their structure or function until recently. Most of the earlier informa- 

 tion is summarized in the monographs of Guilliermond, 143 Macheboeuf, 144 



137 M. L. Quaife, N. S. Scrimshaw, and O. H. Lowry, /. Biol. Chem., 180, 1229-1235 

 (1949). 



138 A. Emmerie and C. Engel, Rec. trav. chim., 58, 895-902 (1939). 



i3D -\y. F. J. Cuthbertson, R. R. Ridgeway, and J. C. Drummond, Biochem. J., 84, 

 34-39 (1940). 



140 S. R. Ames and H. A. Risley, Ann. New York Acad. Set., 52, 149-155 (1949). 



141 K. C. D. Hickman, Biological Antioxidants, Trans. First Conference on Biological 

 Antioxidants, New York, Oct. 10-11, 1946; "General Discussion on Tocopherols as 

 Biological Antioxidants," pp. 78-81. 



142 K. C. D. Hickman and P. L. Harris, Advances in Enzymologij, Vol. VI, Interscience, 

 New York-London, 1946, pp. 469-524. 



143 A. Guilliermond, Les constituants morphologiques du cytoplasme, Hermann, Paris, 

 1934, Chap. VII. 



144 M. A. Macheboeuf, Etat des lipides dans la matiere vivante, Les cevapses et leur 

 importance biologique, Hermann, Paris, 1937. 



