Acetone Metabolism 241 



from the labelled positions of the glycerol. Control deter- 

 minations on the unfermented glycerol were found not to 

 yield formaldehyde. Formaldehyde has also been isolated 

 from resting cell fermentations to which no pool of unlabelled 

 formaldehyde was added. A similar attempt to demonstrate 

 the formation of formaldehyde from uniformly labelled 

 glucose gave no activity in the residual formaldehyde pool. 



When [1, 3-^*C]-glycerol was fermented and the propionate 

 was isolated, the distribution pattern in the propionate was 

 as follows: — 



CH3 - CH2 - COOH 

 HQi^CHg • CHOH • i^CHgOH 397 403 675 



The succinate contained 525 counts/min./mg. C in the car- 

 boxyl group and 425 counts/min./mg. C in the methylene 

 carbons. The distribution is strikingly similar to that 

 observed when labelled formaldehyde was added to the 

 fermentation. This again suggests that glycerol may be 

 metabolized via formaldehyde. 



Although no attempt will be made at present to consider 

 the details of the mechanism of the propionic acid fermen- 

 tation, it is tempting to suggest that formaldehyde may play 

 an important role in the fermentation of 4 and 5 carbon 

 polyalcohols. In these fermentations propionate and some 

 succinate are the major products, and it seems obvious that 

 there must be extensive cleavage and resynthesis. Isotope 

 dilution experiments done by Leaver indicate that CO 2 is not 

 turned over in sufficient quantity to suggest that it has a 

 major role as a synthetic unit in these fermentations. Perhaps 

 formaldehyde assumes this role. - 



It is interesting that serine and propanediol with animals 

 and glycerol with bacteria yield "formate" or formaldehyde. 

 One is reminded of the fact that oxidation of these com- 

 pounds with periodic acid gives formaldehyde from the 

 primary carbinol of each. One wonders whether there may 

 not be an analogous biological oxidation, so that compounds 

 which are activated and contain two adjacent hydroxy Is or 



ISOTOPES 17 



