ACETIC ACID AND ACETATE 275 



shown to exist in yeast, since both citrate and succinate accumulated when 

 acetate was the sole nutrient. ^^^ Moreover, when deuterioacetate was 

 employed, the citrate and succmate were found to contam approximately 

 50% of the original deuterium concentration in bound form.^^* Ljmen^'* 

 also demonstrated that the citric acid cycle was involved in the formation 

 of succinate from acetate. Inasmuch as the inhibition of malonate syn- 

 thesis is overcome by additional oxaloacetate or fumarate, the participation 

 of C4 acids is required in acetate synthesis (wdth the formation of a Ce 

 acid). Wieland and Rosenthal'"' were able to obtain maximum yields of 

 citric acid when acetoacetate and oxaloacetate were incubated in the 

 presence of kidney brei; these authors actually established the identity 

 of the newly-formed citric acid by dii-ect isolation. Two molecules of extra 

 citric acid were formed for each mole of acetoacetate which disappeared.^*^ 

 Lehninger" was able to account for all carbon as acetoacetate when octanoic 

 acid was oxidized with washed rat liver cells; however, when fumarate 

 was present, the citrate and a-ketoglutarate were shown to accumulate 

 at the expense of the acetoacetate. The formation of labeled citrate from 

 acetoacetate has also been demonstrated by Weinhouse et aL^" 



One remarkable feature of the disappearance of acetate from the medium 

 is the importance of other metabolites present in the incubation medium. 

 The presence of added oxaloacetate markedly increases the removal of 

 the acetate and the rate of synthesis of citric acid by yeast. ^'*^ Buchanan 

 and co-workers^** likewise reported the stimulatory effect of citrate, 

 a-ketoglutarate, and of the several C4-dicarboxylic acids on the aerobic 

 disappearance of acetoacetate in contact with kidney homogenates. 

 Although the stimulatory effect on the formation of citrate is exhibited not 

 only by oxaloacetate but also by succinate, malate, and fumarate, Bloch^ 

 opines that the effect is attributable m all cases to oxaloacetate. 



Although acetate and acetoacetate are generally considered to function 

 in an identical mamier m the Krebs cycle, this condition does not invariably 

 obtain. "WTien variations do occur, acetoacetate is usually the more re- 

 active molecule. Thus, in the balance studies with kidney preparations, 

 140,141 Q^^ ^yQii as in a heart muscle preparation," only acetoacetate was 

 found to be a precursor of citrate. Under such conditions acetylphosphate 



»39 F. Lynen, Ann., 654, 40-68 (1943). 

 '« H. Wieland and C. Rosenthal, Ann., 554, 241-260 (1943). 

 '*'■ F. E. Hunter and L. F. Leloir, J. Biol. Chem., 159, 295-310 (1945). 

 i« R. Sonderhoff and M. Deffner, Ann., 536, 36-43, 44-50 (1938). 

 '" J. M. Buchanan, W. Sakami, S. Gurin, and D. W. Wilson, /. Biol. Chem., 159, 

 695-709(1945). 



