■rrRXOVEE 15AIK OF T1{E FATTV AflDS OF 1111; IIVER 405 



fatty acids contiihiilo in 1hrs(> long-time expoiimonts significant quanti- 

 ties of labelled acetyl groups 1o the acelic acid pool which supplies i^C 

 to the newly formed fatty acid molecules. 



Th(> saturated I'atty acids of liver were found to reach half of their 

 maximal isotope concentration in less than 1 day, Ihe unsaturated acids 

 in al)0ul 2 days. Much longer time is necessary to reach a corresponding 

 i^C concentration in the fatty acids of the carcass, 16 — 17 days for 

 saturated and 19 — 20 days for the unsaturated acids. This difference 

 was also shown in recent work of Popjak and Beeckmans(^). 



In an investigation on the effect of changes in the metabolic rate on 

 the incorporation of ^'*C into tissue fractions, we determined the specific 

 activity of the liver fatty acids of the mouse following injection of 

 carboxyl labeled acetate in experiments of 10 to 180 min duration. The 

 results obtained, which are discussed in this note, suggest, the existence 

 of a fatty acid fraction in the mouse liver of much shorter half-life than 

 about 1 day. which was found in the various experiments mentioned 

 above. 



EXPERIMENTAL 



In each experiment 45 to 72 mice were injected intraperitoneally 

 with 0.2 ml of 0.8% sodium chloride solution containing 2 — 4 microcurie 

 (0.2—0.4 mgm) of sodium acetate labelled in the carboxyl group. The 

 animals were divided in 5 — 6 equal groups and killed after 5 to 240 

 min. 



The pooled organs were frozen in solid COg. The ground tissue was then 

 extracted for 3 hr with a boiling mixture of ether-alcohol 1:3. The filtrate 

 obtained was evaporated in vacuo and the residue extracted with pet- 

 roleum-ether. The residue obtained after evaporation of the petroleum- 

 ether was saponified for 8 hr with 10 ml of 40% KOH solution and 20 

 ml of alcohol on a boiling waterbath. 



The solution was extracted three times with petroleum-ether in order 

 to remove the insaponifiable matter. The aqueous solution was then 

 neutralised with 40% HoSO^ solution and extracted three times with 

 petroleum-ether. 



The petroleum-ether solution on evaporation gave the fatty acids. 

 The determination of the radioactivity was carried out with a Geiger 

 counter, 8 mgm of each sample on an aluminium disk of 5 mm diameter. 



(i^G. Popjak and .M. L. liEEOKMANS, Biochem. J. 69, o47 (19.50). 



