TURNOVER RATE OF THE FATTY ACIDS OF THE LIVER 



40: 



specific activity should bo al)()ut 3% only. Wo assumed in \\w above 

 calculation that all formation of lal)olled fatty acid molecules ceases 

 after the lapse of 30 min. As this assumption does not hold strictly, the 

 decline in the specific activity of fatty acids in the interval between 30 

 and 60 min. is even less than 3%. 



The data of Fig. 1 indicate a very much larger decrease in the specific 

 activity of the fatty acids than 3% in the interval between 30 and 60 



40 



60 



80 



100 



120 



180 



240 



Time, minures 



Fig. 2. Change of the specific activity of the brain fatty acids with 



time. 



min after administration of the labelled acetate. The decrease amounts 

 to about 50%. These results suggest the presence of a rapidly renewable 

 fatty acid fraction in the liver of the mouse. 



In experiments in which the labelled acetate is fed for days and the 

 specific activity of the fatty acids in the liver daily determined, the 

 presence of a minor fraction of rapid renewal rate cannot be expected 

 to be observed. 



We investigated also the change of the specific activity of the brain 

 fatty acids and muscle fatty acids with time. The specific activity of the 

 brain fatty acids was found, as seen in Fig. 2, to increase rapidly with 

 time in the course of the first minutes and then to remain almost constant. 

 We lack thus any indication of the presence of rapidly renewed fatty 

 acid faction in the brain. The specific activity values of the muscle 

 fatty acids extracted from different groups of mice fluctuate consi- 

 florably. An indication of a decrease of the specific activity figures 

 within a 240 min. observation period is, however, also in this case absent. 



Summary 



Following the injection of in its carboxyl group labelled acetate to mice, the 

 specific activity of the fatty acids extractes from the liver after the lapse of 30 

 minutes is found to be appreciably lower than measured a few minutes after injec- 

 tion. It follows from this finding that the fatty acids of the liver contains a rapidly 

 renewable fraction. 



