BIOSYNTHESIS OF PENTOSES IN ESCHERICHIA COLI

Abstract

Previous studies have shown that Escherichia coli possesses two principal pathways for the biosynthesis of pentose from hexose. The best known involves the decarboxylation of 6-phosphogluconate to ribulose 5-phosphate. This is the principal pathway in E. coli grown on glucose (Lanning and Cohen, 1954; Bernstein, 1956). This pathway will be referred to as the oxidative pathway. (The term oxidative pathway is used here to describe the formation of pentose by the oxidative decarboxylation of 6-phosphogluconate and excludes any resynthesis by a complete pentose cycle. The stoichiometry is: 3 hexose + oxygen 3 pentose + 3 CO2. The term transketolasetransaldolase pathway is used here to indicate nonoxidative synthesis of pentose from hexose,

Pentose synthesis in Escherichia coli

“…This shows that little, if any, randomization occurred via the transketolase-transaldolase reactions. This is in agreement with the results of other workers who studied the 14C distribution of the glucose of glycogen isolated from E. coli grown in the exponential phase on [2-14C]glucose (Szynkiewicz et al, 1961;Sable and Cassisi, 1962). The small redistribution of 14C suggested that there was only 1-2% randomization of the hexose carbon skeleton.…”

“…The interpretation of these results led to estimations of between 10 and 80% for the relative participation of the oxidative pathway for ribose synthesis in E. coli. This wide range was due, in part, to the fact that the activities of pathways varied considerably with the conditions of growth (Szynkiewicz et al, 1961; Model and Rittenberg, 1967) and, in part, to the many assumptions made in the calculation of the results.…”

Oxygen-18 studies on the oxidative and nonoxidative pentose phosphate pathways in wild-type and mutant Escherichia coli cells

“…The same conclusion was reached by Rittenberg and Ponticorvo (1962) and Model and Rittenberg (1967) on the basis of the C coproduction from [l-180]glucose and glucose in wildtype E. coli cells. Sable and coworkers (Sable and Cassisi, 1962;Szynkiewicz et al, 1961) arrived at the same conclusion from a study of the distribution of 14C in glucose isolated from the glycogen of wild-type E. coli which was grown on [2-14C]glucose. In this organism, where there is no nonoxidative pathway, one cannot make any conclusions regarding model I or model II.…”

“…The conversion of 14C-labeled substrates to the pentose phosphate moieties of DNA and RNA has been used to estimate the relative contribution of both pathways (Bagatell et al, 1959;Sable and Cassisi, 1962;Wood et al, 1963). It was shown (Szynkiewicz et al, 1961;Model and Rittenberg, 1967) that the activities of the two pathways varied considerably with the conditions of growth of the organism. The 14C data from E. coli and other organisms were interpreted by some laboratories (Horecker and Mehler, 1955;Horecker, 1965;Sable, 1966;Caprioli and Rittenberg, 1969) to suggest that the oxidative and nonoxidative pathways operate simultaneously to synthesize pentose phosphate for nucleic acid biosynthesis and estimates were made of the contribution of each pathway.…”

The Labeling of Pentose Phosphate from Glucose-14C and Estimation of the Rates of Transaldolase, Transketolase, the Contribution of the Pentose Cycle, and Ribose Phosphate Synthesis*

“…Alternately, a computer program was set up for finding such values.8 (A) Bacteria. Sable and co-workers (Szynkiewiz et al, 1961;Wright et al, 1961;Sable and Cassisi, 1962) studied synthesis of ribose and desoxyribose by E. colt, grown on labeled precursors, in a variety of conditions. They observed that the labeling pattern is variable, depending on the carbon source in the medium, the stage of growth, and the previous history of the culture.…”