Heavy Carbon as a Tracer in Heterotrophic Carbon Dioxide Assimilation*

The first proof that heterotrophic, non-photosynthetic bacteria can fix carbon dioxide was presented in 1935 by Wood and Werkman (15). This investigation introduced the first experimental evidence that carbon dioxide serves as a building material in synthetic reactions of all forms of life, whether simple or complex. The synthesis of citric acid from oxalacetate by avian tissue was shown by Krebs and Johnson in 1937 (8), and Wood and Werkman (17) suggested that this reaction involved utilization of carbon dioxide. The recent results of Evans and Slotin (7) with radioactive carbon (Cll) provide the experimental evidence showing that this is the case. The California group (Barker et al. (1, 2); Ruben and Kamen (14) ; Carson and Ruben (6) ; Carson et al. (5)), using CF, has confirmed and extended our knowledge of heterotrophic carbon dioxide assimilation. They demonstrated fixation of carbon dioxide with yeast and a number of heterotrophic bacteria. The present report concerns the mechanism of carbon dioxide fixation. Heavy carbon (Us) has been used as a tracer of fixed carbon dioxide. Such studies undoubtedly will lead to a clearer understanding of the chemistry of photosynthesis and chemosynthesis in general. The present results show the distribution of fixed carbon dioxide in the products of bacterial fermentation (19).