VOL. 12 (1953) BIOCHIMICA ET BIOPHYSICA ACTA 207 



CO2 TURNOVER IN THE FERMENTATION OF 3, 4, 5 AND 6 

 CARBON COMPOUNDS BY THE PROPIONIC ACID BACTERIA* 



by 



HARLAND G. WOOD and F. W. LEAVER** 



Department of Biochemistry, Western Reserve University School of Medicine, 



Cleveland, Ohio (U.S.A.) 



The principal products of fermentation of glucose, glycerol, and lactate by the pro- 

 pionic acid bacteria are propionate, acetate, succinate, and carbon dioxide. The following 

 schematic diagram represents the most generally accepted mechanism by which these 



substrates are fermented. 



Acetate + COg 



t 



„ , Embden-Meyerhof Scheme r, j_ + CO, 

 Glucose > Pyruvate > 



t 11 



Glycerol Lactate 



Oxalacetate — ^— ^ '- — > Succinate — -> Propionate + COg 



Fig. I 



The evidence for this mechanism of dissimilation of glucose and glycerol rests 

 mainly upon the following observations : 



First, several of the intermediate compounds of the Meyerhof scheme have been 

 isolated from the fermentations of glucose and glycerol^-^-^, and have been shown to 

 be utilized. Second, it has been shown that oxalacetate can be converted to succinic 

 acid*, and that succinic acid is decarboxylated to propionic acid and COg^'^''^. Third, 

 ^^COg was incorporated into the carboxyl carbons of succinate and propionate and the 

 dilution of the final ^^COg by ^^COg arising from the substrate was of the proper magni- 

 tude to be explained by the above scheme^. 



However, several workers have pointed out that the scheme is not a complete 

 explanation of the fermentation mechanism. Werkman et al.^ have suggested that in 

 addition to the Meyerhof scheme there is a second mechanism of glucose fermentation 

 which is not fluoride sensitive. The scheme of Fig. i also is not entirely adequate be- 

 cause it indicates that the molar quantity of COg should be equal to or less than the 

 acetate, whereas in some fermentations the COg is much greater than the acetate^". To 

 account for this it has been proposed that the Cg compound is in some way converted 

 to succinate possibly by direct condensation^ '^^ or via the Krebs cycle^^. 



* Supported in part by grants from the Atomic Energy Commission and the Prentiss Foundation 

 of Western Reserve University. The isotopes used in this investigation were received on allocation 

 from the Atomic Energy Commission. 



** Postdoctoral Fellow, National Institutes of Health. Present address : Department of Biochemis- 

 try, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania. 



References p. 22i\222. 



