Acetone Metabolism 239 



amount in the carboxyl groups. Since CO 2 is fixed only in 

 the carboxyl group it is evident that the formaldehyde was 

 not used in the form of CO 2. The formaldehyde was added 

 to a resting cell fermentation in -001 m. concentration and 

 contained 142,000 counts/min./mg. C. Almost one-half of 

 the added activity was recovered in the propionic acid. 

 Additional activity was found in the succinate and CO2, and 

 a small amount in the acetate. The succinate was labelled 

 in both the carboxyl and methylene positions, but did not 

 always have a distribution similar to that in the propionate. 

 The reactions by which the fixation of formaldehyde occurs 

 are obscure, but this discovery certainly opens up new possi- 

 bilities of revealing the mechanism and of studying the 

 propionic acid fermentation. It has never been completely 

 certain how propionate is formed in this fermentation and 

 the interrelation of succinate and propionate has remained 

 an interesting problem. Although there is evidence that 

 propionate may be formed by decarboxylation of a C4 dicar- 

 boxylic acid, it is not at all certain that this is the major 

 pathway of its formation (Wood, 1942; Delwiche, 1948, 1950). 

 In this connection it is of interest that either a or ^8 labelled 

 propionate yields equal labelling in the 1, 2, 5, 6 positions of 

 rat liver glycogen (Lorber, Lifson, Sakami and Wood, 

 19506). These results are quite different from those with a 

 or j3 labelled lactate, with which the labelling is always 

 unequal in the 1, 2, 5, 6 positions, apparently because of direct 

 conversion of the lactate to glycogen (Lorber, Lifson, Wood, 

 Sakami and Shreeve, 1950a). Apparently with propionate 

 there is little or no direct conversion, and the conversion to 

 glycogen involves complete randomization of the a or jS 

 carbon of propionate. Perhaps the reason this occurs will 

 be revealed when we understand more about the reactions 

 whereby propionate is formed from glucose in the bacterial 

 fermentation. 



The most recent investigations by Leaver (unpublished) are 

 of further interest because they appear to show that free 

 formaldehyde is formed in the propionic acid fermentation. 



