VOL. 12 (1953) 



CO2 TURNOVER IN FERMENTATION 



213 



carboxyl group to ^^COg. Possibly the C^ formed during the decarboxylation of the 

 C4-dicarboxylic acid remains linked with CoA and thus does not equilibrate with the 

 CO 2- This problem will be discussed further in relation to the CO 2 turnover studies. 



Although the assumption that there is no significant secondary conversions of the 

 end products which will cause a change in the ^*C concentration of the CO 2 isnot valid, for 

 purposes of the present investigation the error is not serious. It is seen in Tables VIII 

 and IX that the carboxyl groups of the propionate and succinate always contain less 

 activity than the final ^^COg. There is little or no net change in the amount of propionate 

 or succinate under conditions in which the a and jS carbons of propionate are randomized. 

 Thus if the exchange of ^^COg with the carboxyls of propionate and succinate occurs by 

 this conversion, it will introduce ^^C into the carboxyls and decrease the ^^C in the COg. 

 Thus it will decrease Xf. It is apparent from Equation i that this will increase the 

 value of A and thus the calculated CO 2 used s-i^d COg total will be higher than that which 

 would have been obtained if no secondary reactions were occuring. Since the principal 

 conclusion made from the CO 2 turnover studies is that the CO 2 total or CO 2 produced is 

 lower than predicted from generally accepted concepts of the fermentation, the error 

 will not favour or invalidate these conclusions. It therefore seems justified to use the 

 calculation with due realization of limited accuracy. 



The validity of the assumption of equilibration of the CO2 inside and outside of the 

 cell has not been tested. If equilibrium is not attained, the calculated COg used will be 

 low since less i^C02 will be taken up by the cell and therefore the dilution of the ^^COg 

 would be less than assumed for the calculation. 



Nothing has been done to determine whether the cells distinguish between ^^C 

 and ^^C, although this is known to occur in some reactions. 



The above discussion serves to emphasize the difficulties that must be confronted 

 in turnover studies. It is to be noted that the present conditions involving a unicellular 

 organism in a homogeneous suspension in a controlled atmosphere in a closed system 

 are more favourable for such studies than is possible in many investigations. 



CO 2 turnover and fixation ivith j, 4 and 5 carbon compounds. The calculated values 

 for CO 2 utilization and production during fermentation of 3, 4, and 5 carbon compounds 

 are shown in Table VI and the distribution of the fixed ^"^C in the products in Table VII. 



TABLE VI 



14r 



COg TURNOVER CALCULATED FROM "COg DILUTION 



nMjioo mM substrate 



^ , , , J Calculated 



Calculatea „^ ^^ >, j j 



CO. J CO^oi,^„^,^ CO ^produced 



(T ('') ^""^^ total) 

 '-"' (a + b) 



No. 



Substrate 



mM zoo/ ml 



mA 



cpm 1.1 M 



Substrate 

 fermented 



Initial 

 CO. 



Final 

 CO^ 



Initial 

 CO, 



Final 

 CO, 



12 Pyruvate 



1 2 Glycerol 



14 Erythritol 



15 Adonitol 



7.04 

 6.95 

 4-33 



7-45 



1. 16 



2.27 

 2.31 



2.27 



5-59 

 1. 81 

 2.58 

 3.81 



83.8 

 78.4 

 83.8 

 78.4 



15.8 

 65.2 



53-7 

 23.8 



3-8 

 12.0 



18.6 

 26.8 



63.0 



— 6.6 



6.2 



20.7 



66.8 



5-4 

 24.8 



47-5 



(a) Calculated by Equation i. 



See Table III and Table VII for additional data on these fermentations. 



The calculated values for CO 2 produced from glycerol, erythritol and adonitol were 

 respectively 5.4, 24.8 and 47.5 mM per 100 mM of fermented substrate. It is seen in 

 Table III that approximately 100 mM of propionate were produced per 100 mM sub- 



References p. 221J222. 



