PENTOSE SYNTHESIS IN ESCHERICHIA COLI

Escherichia coli was grown on [1-18O]-, [2-18O]-, and [6-18O]glucose and [2-18O]fructose as the sole carbon sources. Growth was terminated in midexponential phase and the nucleic acids were isolated and degraded to the nucleoside level. The distribution of 18O in the nucleosides was determined in a mass spectrometer by observing mass shifts of fragment ions in the mass spectrum of the nucleosides. A fragment ion containing 18O exhibits a peak in the mass spectrum 2.0043 mass units higher than the normal ion containing 18O. The relative intensities of the peaks can be related to the per cent 18O in the fragment. When [1-18O]- and [6- 18O]- glucose were used as carbon sources, 35 and 64%, respectively, of the original label of the hexose appeared in the 5′-oxygen atom of the nucleosides. No other oxygen atoms were labeled. When [2- 18O]glucose and [2-18O]fructose were used as the substrates, the ribosides were similarly labeled with approximately 14% of the original label of the hexose in the 2′ position and 22% in the 4′ position (the deoxyribosides contained 18O only in the 4′-oxygen atom). These results show that both the oxidative and nonoxidative pathways operate simultaneously to produce pentose phosphate. The major portion (about 70%) of the pentose in the nucleic acids was synthesized via the nonoxidative pathway and the remainder via the oxidative pathway. The above experiments also provide evidence which suggests that the enzyme aldolase in E. coli, in contrast to that of mammalian muscle, cleaves fructose 1,6-diphosphate without the obligatory loss of the C-2 oxygen atom. © 1969, American Chemical Society. All rights reserved.