Utilization of carbon dioxide in the synthesis of proteins by Escherichia coli. I.

Since carbon dioxide is always present in living systems where synthesis of proteins is occurring, it is desirable to study the fate of tracer isotopes of this rather simple metabolite before turning to more complicated substrates. Metabolic activity of most organisms leads to formation of COz which in many cases is subsequently incorporated into amino acids, purines, pyrimidines, and other biologically important compounds. The studies leading to formulation of the Wood-We&man reaction (1) demonstrated the importance of carbon dioxide as a participant in metabolism of heterotrophic organisms. Later investigations by Ruben and Kamen (2) and Evans and Slotin (3) indicated that carbon dioxide is utilized by mammalian tissues. The incorporation of isotopic carbon into proteins of mammalian liver was first demonstrated by Delluva and Wilson (4), who studied fixation of Cl3 derived from NaHC1303 and found the isotope in aspartic and glutamic acids and arginine. These workers were hindered in their investigation by relatively low metabolism of the organisms used and the unavoidable dilution of the isotopic carbon with inactive carbon. Anfinsen et al. (5) have studied incorporation into liver slices of Cl4 derived from NaHCLq3. They also found isotopic carbon in aspartic and glutamic acids and arginine. Ehrensviird (6) has studied incorporation of Cl302 by the yeast Torulopsis utilis and has found isotopic carbon in the three amino acids already mentioned and lesser amounts in other amino acids. We have investigated the metabolism of Escherichiu coli in the presence of Cl402 and have found that as much as 50 per cent of the isotopic tracer added to the medium was fixed by the organisms. Two-dimensional paper chromatograms of hydrolysates of these organisms followed by radioautographs revealed at least sixteen different radioactive components. Studies have been made to determine the components into which the Cl4 was synthesized. It has been possible to account for most of the radioactivity in proteins and nucleic acids. Isotopic carbon has been found in amino acids from protein hydrolysates including aspartic and glutamic acids, arginine, lysine, proline, and threonine. The location of isotopic tracers in these amino acids has been partially determined.