22 BACTERIAL FERMENTATIONS 



After the fate of the carbon atoms of acetate was estab- 

 lished, it became of interest to find out what happens to 

 the hydrogen atoms attached to the methyl group. In par- 

 ticular, it was important to determine whether some or 

 all of these hydrogen atoms are removed by an oxidative 

 reaction during the course of the fermentation of acetate 

 or whether the methyl group is incorporated intact into 

 methane. This question was investigated by Pine. 27 In 

 the experiment illustrated by equation 12 acetate labeled 



CD3COOH -5$. CD 3 H + co 2 (12) 



in the methyl group with deuterium was fermented and the 

 amount of deuterium per mole in the evolved methane was 

 compared with that in the substrate. Mass analysis showed 

 that the deuterium contents of the acetate and methane 

 were essentially equal. In another experiment illustrated 

 by equation 13 unlabeled acetate was fermented in the 



CH3COOH -2£ CH 3 D + co 2 ( 1 3) 



presence of D 2 0. The data indicate that approximately 

 one atom of deuterium per molecule of methane was de- 

 rived from the solvent. These results demonstrate that 

 the methyl group is transferred from acetate to methane 

 as a unit, without the loss of attached hydrogen or deu- 

 terium. In other words, one or more transmethylation 

 reactions occur during the fermentation. 



Pine 28 later investigated the same problem with methanol 

 by allowing unlabeled methanol to ferment in the presence 

 of a mixture of D 2 and H 2 (equation 14) . The meth- 

 ane formed in this experiment contained a large percentage 

 of CH 3 D, although somewhat less than the percentage of 

 deuterium in the water. This was interpreted to mean 



