TRIGLYCERIDES AND FATTY ACIDS 201 



which the pahnitic add was labeled with C^"* at the carboxyl group or at 

 carbons ^ or //, respectively, expired C^'^Oi at the same rate. This means 

 that, once the process of breakdown of palmitic acid is initiated in the in- 

 tact rat, the molecule is disrupted in such a manner that all its carbons are 

 converted to CO2 at about the same time. This precludes the existence of a 

 major portion of the carbon from palmitic acid as a stable intermediate of 

 oxidation ;^'''^ the number of molecules which become stabilized as lauric or 

 myristic acid are few as compared with those completely oxidized. Lerner 

 and associates'' '^ reported that approximately 36 to 59% of the C^^02 

 originating from palmitic acid labeled with C^'* at its sixth carbon was 

 eliminated within twenty-four hours after its intravenous injection. 



In studies on labeled stearic acid, Weunnan and collaborators'''^ found 

 some differences in the rate of utilization of the carboxyl carbon from that 

 of the sixth carbon. Thus, after the injection of tristearm-1-C'^ into fasted 

 rats, 40 to 44% of the C''*02 was eliminated during the first twenty-four 

 hours, as contrasted with only 30 to 38% of the labeled carbon as C^''02 

 after the injection of tristearm-6-C'^ It was also found that some iso- 

 topically marked tripalmitin was present in the body fats, although the 

 activity of the 18-carbon fraction was tw^elve times as great as that of the 

 16-carbon fraction. The authors, therefore, interpret the differences in the 

 rate of excretion of C^^02 to mean that some of the tristearin-6-C'* becomes 

 stabilized at the palmitic acid stage, thus lessening the proportion available 

 for complete oxidation of the molecule. Although the same change will 

 obviously occur in the tristearin-1-C'^, it has already ehminated the C* 

 from its molecule. 



Ascorbic acid was shown by Rusch and Klein^^' to play a role in the oxida- 

 tion of emulsions of liver phospholipids. Abramson^'^ reported that the 

 oxidation of unsaturated fatty acids, as measured by the thiobarbituric acid 

 reaction, was highest in the brain, nerve, and testis of normal guinea pigs; 

 on the other hand, in the scorbutic guinea pig, oxidation was decreased in 

 brahi, testis, medulla oblongata, adrenal, and kidney, whereas it was un- 

 changed from the normal in the liver, spleen, and heart. This decreased 

 oxidation rate of unsaturated fats m scorbutic tissues could be corrected by 

 the addition of ascorbic acid in vitro. When vitamin C was added to the 

 tissues of normal animals, the oxidation rate was decreased in the liver, in- 



^15 S. R. Lerner, I. L. Chaikoff, C. Entenman, and W. G. Dauben, Proc. Soc. Exptl. 

 Biol. Med., 70, 384-387 (1949). 



"6 E. O. Weinman, I. L. Chaikoff, B. P. Stevens, and W. G. Dauben, J. Biol. Chem., 

 191, 523-529 (1951). 



'" H. P. Rusch and B. E. Klein, Cancer Research, 1, 465-472 (1941). 



"8 H. Abramson, /. Biol. Chem., 178, 179-183 (1949). 



