THE NATURE OF BLOOD LIPIDS 367 



are of the opinion that the protein associated with the 0-carotene is a 

 globulin, and probably a /^-globulin. Using the method of fractional pre- 

 cipitation, Pett and LePage 117 also reported that carotene in serum (pre- 

 sumably human) is bound with the globulin fraction. Oncley and associ- 

 ates, 76 and Cohn et al. us reported the presence of carotenoids in a lipo- 

 protein. Ganguly, Krinsky, Mehl, and Deuel 6 found that carotenoids 

 and vitamin A are carried by different protein fractions in the blood. In 

 the case of beef plasma, which contains /3-carotene, the carotenoid was found 

 with the more soluble protein fraction (presumably the albumin), along 

 with lutein and vitamin A alcohol. 



However, there is some question as to whether or not the fact that the 

 carotenoid is non-extractable may be taken as proof that the carotene is 

 combined with a protein. Thus, Van den Bergh and Miiller 119 reported 

 that simple aqueous colloidal solutions of carotene resembled blood caro- 

 tene in that they were not readily extracted by organic solvents such as 

 ether, although there was no protein to hold the carotene in combination 

 in this case. These observations were confirmed by Drummond and 

 McWalter. 120 On the basis of this experimental evidence, these workers 

 considered that carotene exists in serum in simple colloidal solution. Al- 

 though Dzialoszynski et al. 112 likewise confirmed the fact that colloidal 

 carotene became unextractable when it was added to normal plasma, 

 it was further shown that it remained readily extractable provided the 

 protein in the plasma had been denatured previous to the addition of the 

 carotene, by shaking with ether. 



However, there are additional facts which favor the concept that an 

 actual carotene-protein combination exists in blood. For example, such 

 complexes of protein with carotenoids are widespread in nature. These 

 include the lycopene-protein complex in tomato, 121 rhodopsin in the retina, 

 described by Wald, 122 the vitamin A ester and protein combination found 

 by Lovern and Morton 123 in the tunica propria of fish intestines, and the 

 astaxanthin-protein compound in lobsters discovered by Kuhn and S0ren- 



117 L. B. Pett and G. A. LePage, J. Biol. Chem., 132, 585-593 (1940). 



118 E. J. Cohn, F. R. N. Gurd, D. M. Surgenor, B. A. Barnes, R. K. Brown, D. Derou- 

 aux, J. M. Gillespie, F. W. Kahnt, W. F. Lever, C. H. Liu, D. Mittelman, R. F. Mouton, 

 K. Schmid, and E. Uroma, J. Am. Chem. Soc, 72, 465-474 (1950). 



119 H. H. Van den Bergh and P. Muller, Proc. Acad. Sci. Amsterdam, 22, 748-757 

 (1920). 



120 J. C. Drummond and R. J. McWalter, /. Physiol., 83, 236-242 (1935). 



121 R. Kuhn and H. J. Bielig, Ber., 73, 1080-1091 (1940). 



122 G. Wald, /. Gen. Physiol, 21, 795-832 (1937-1938). 



123 J. A. Lovern and R. A. Morton, Biochem. J., 33, 330-337 (1939). 



