Dark Fixation of CO2 by Tobacco Leaves.

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Abstract
Excised leaves of N. tabacum have the ability to incorporate C14O2 into several organic and amino acids. These compounds have been identified by paper chromatography. The initial fixation of C14O2 appears to be mediated by the enzyme phosphoenolpyruvate carboxylase. The presence of this enzyme in tobacco leaves is described. The pattern of labeled compounds obtained in the dark fixation suggest the operation of the Krebs cycle and concomitant transaminations. No carbohydrates or phos-phorylated sugars are labeled after extended periods of dark incorporation of C14O2. Thus, light is needed to furnish all of the reducing power to reverse glycolytic processes.