The Nonphotosynthetic Fixation of Carbon Dioxide by ThreeMicro-Organisms

Studies by Lynch and Calvin (1952,1953) have established the nature of the compounds incorporating C{sup 14} nonphotosynthetically from C{sup 14}O{sub 2} in thirteen microorganisms: a yeast, a protozoan, two water moulds, one slime mould, three algae, three bacteria, and the green flagellate Euglena Gracilis. With the exception of H. gracilis, and of Lactobacillus cassi which fixed no detectable amounts of carbon dioxide, all these organisms fixed carbon dioxide into amino and organic acids derived from the tricarboxylic acid cycle, and into a few other compounds in individual cases (tyrosine, phenylalanine, polysaccharides [probably glucose polymers], acetic acid and butyric acid). The authors concluded that the presence of C{sup 14} in almost all these compounds could be accounted for by the carboxylation of pyruvate to yield oxalacetic or malic acids, followed by transaminase reactions. In E. gracilis, however, considerable quantities of activity also appeared in phosphorylated compounds in the dark, especially in the sugar monophosphates, phosphoglyceric acid, and phosphoenolpyruvic acid. Only with this organisms was a kinetic study performed to determine the identity and degree of labeling of the compounds containing C{sup 14} after varying periods of time. It was not stated definitely by which route carbon dioxide entered the photosynthetic intermediates, but it was implied that it was incorporated directly into phosphoglyceric acid, and that the energy for this process, which in photosynthesis is derived from sunlight, and was provided by respiration or fermentation. Certain aspects of these presumptions however, do not adequately account for all the experimental data