THE NATURE OF BLOOD LIPIDS 369 



jects, a maximum of as much as 90% of the total vitamin A appeared in 

 this fraction after large doses of vitamin A had been ingested. 



In contradistinction to the increase in ester when vitamin A is fed, a rise 

 in the alcohol fraction was noted by Hoch 131 as a consequence of the mobili- 

 zation of endogenous vitamin A. Thus, after the ingestion of alcohol, the 

 vitamin A alcohol in the blood was increased. 



Glover and associates 132,133 reported that the plasma vitamin A level in 

 rats is proportional to the amount of free vitamin A alcohol in the liver, but 

 not to the total stores in this organ, which consist primarily of vitamin A 

 esters. However, the recent studies of Ganguly et al. lu showed opposite 

 results from those of Glover and co-workers, 133 and no correlation could be 

 drawn between the unesterified vitamin A in the liver and the level of 

 plasma vitamin A. Further investigations are necessary to clarify the 

 reasons for the divergent results in these two groups. 



According to the recent report of Ganguly et al., 6 not only is (S-carotene 

 associated with a protein in the plasma, but the same is true for the vitamin 

 A alcohol and the vitamin A esters. Furthermore, it was demonstrated 

 that the two vitamin fractions are associated with separate proteins. 

 Rajagopal and Datta 126 reported that, in normal human plasma, 120-200 

 I.U. of vitamin A is associated with 6 to 8 g. of protein. 



Krause and Alberghini 135 demonstrated that a factor capable of hydrolyz- 

 ing vitamin A esters occurs in the blood of man, rats, and rabbits. The 

 factor was shown to be present in the serum and plasma of blood, but not 

 in the cellular elements. 



(b) Vitamins D. Although it is certain that the vitamins D are present 

 in the blood and that the amount and type must vary with the diet and 

 with the species of animal, any specific information as to these vitamins 

 must await the development of adequate methods for their determination 

 and identification. 



(c) Vitamins E {Tocopherols). There are four tocopherols which occur 

 naturally in the ordinary vegetable fats, namely, a, (3, y, and 8. Quaife 

 et a?. 136 have demonstrated that d-a-tocopherol is absorbed preferentially 

 by the human subject, as compared with d-7-tocopherol. The a-isomer 

 also appears to be the compound which possesses the highest vitamin E 

 activity and the lowest antioxidant potency. Under normal conditions, 



132 J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. J., 40, lvii (1946). 



133 J. Glover, T. W. Goodwin, and R. A. Morton, Biochem. J., 41, 97-100 (1947). 



134 J. Ganguly, N. I. Krinsky, and H. J. Deuel, Jr., Federation Proc., 11, 218 (1952). 



135 R. F. Krause and C. Alberghini, Arch. Biochem., 25, 396-400 (1950). 



136 M. L. Quaife, W. J. Swanson, M. Y. Dju, and P. L. Harris, Ann. New York Acad. 

 Sci., 52, 300-305 (1949). 



