212 H. G. WOOD, F. W. LEAVER VOL. 12 (1953) 



The assumption that there are no secondary conversions of the end products that 

 cause a change in the ^*C concentration of the CO 2 has been investigated and it has been 

 found not to be valid. Experiments testing this point are shown in Table V in which 

 glycerol fermentations were conducted with ^*C-propionate added at the beginning of 



TABLE V 



METABOLISM OF ^*C-PROPIONATE DURING GLYCEROL FERMENTATION 



mM pen 00 1 ml Total counts „, r jj j Distribution of "C in propionate 



\jg LMoeiiea "C in final 



position Initial Initial Final Initial Initial Final „„' cpm per iiM 



propionate CO^ CO^ propionate CO. CO^ ^^^ CH. CH^ COOH 



17 COOH 0.83 12.5 II. o 40,500 o 9,300 23.0 — — 1. 81** 



18* CH3 3.23 12.5 10.8 12,150 000 0.486 0.375 000 



* The distribution of ^*C in the succinate was 0.054 i^i the COOH and 0.540 in the CHg in cpm per 

 fxM. By total carbon the succinate contained 1.165 cpm per j^M, the propionate 0.865 cpm per //M. 



** The propionate was not degraded, all the ^*C has been assumed to be in the carboxyl group. 

 Fermentation No. 23 of Table VIII was set up simultaneously with these fermentations as a 

 control for measurement of COg turnover. The glycerol fermented and mM of products were very 

 similar in the three fermentations. 



The conditions of fermentation were the same as No. 20, 21, 22 of Table VIII except there was 

 60 ml of reaction mixture and in Fermentation 17 propionate- i-^*C (48.9 cpm per ^iM) and in Fer- 

 mentation i8propionate-3-i*C (3.65 cpm per fiM) were added. Time was 40 h. Culture 34W. Proce- 

 dures are given in the text. 



the fermentation. It is seen in Fermentation 17 that 23.0% of the ^^C added as carboxyl 

 labelled propionate was converted to CO 2. The methyl group of propionate was not 

 oxidized to CO2 but it is clear that the propionate was metabolized because the ^"^C was 

 87% randomized in the a and ^ positions (0.375 X 2/0.486 +0.375). The succinate from 

 this fermentation was degraded and it was found to be labelled in the methylene positions 

 with somewhat higher activity than the propionate. The results are thus in accord with 

 the view that the randomization of a and /S carbons of propionate via conversion to a 

 C4-dicarboxylic acid. The higher activity of the succinate than propionate is probably due 

 to the incorporation of high activity propionate early in the fermentation and failure 

 to equilibrate with low activity propionate late in the fermentation. In other experiments 

 which will be published elsewhere it has been found by incubation of resting cells with 

 propionate-3-^^C and succinate, that the isotope becomes completely randomized in the 

 a and ^ carbons of propionate but the succinate only reaches 15% of the activity of the 

 final propionate. This is interpreted as an indication that extracellular succinate may 

 equilibrate with intracellular succinate slower than do the corresponding propionate 

 "pools". The present results are very similar to results obtained independently by 

 Delwiche et al.^^. They have found with an enzyme preparation from propionic acid 

 bacteria that succinate-i,2-^*C is formed from propionate-2-^'*C, ^'COg and unlabelled 

 succinate, but the incorporation of ^"^C from propionate is fifty to sev^enty times that 

 from ^^COg. Likewise the yield of propionate-i-^^C was twenty times that of ^^COg from 

 succinate-i-^*C. ATP and CoA were required for the reaction. Likewise Whiteley^^ 

 has found with extracts of Micrococcus lactilyticus that ATP, CoA and cocarboxylase 

 stimulate the decarboxylation of succinate. From the standpoint of the present discussion 

 the important point is that the exchange of the carboxyl group of propionate with CO 2 

 is slower than is the randomization of the a and ^carbons. It would appear thatrandom- 

 ization via a C^-dicarboxylic acid can occur without equivalent conversion of the 



References p. 221 j 2 22. 



