BIOSYNTHESIS OF PENTOSES IN ESCHERICHIA COLI

Abstract

Synthesis of ribose, deoxyribose and glycogen by E. coli under various conditions of growth was studied with C14 tracers. From the distribution of C14 in the ribose of ribonucleic acid, deoxyribose of deoxyribonucleic acid and glycogen-glucose was calculated the proportion of pentose formed via direct oxidation of 6-phosphogluconate and that formed by nonoxidative synthesis through the transketolase and transaldolase reactions. When acetate is the principal source of carbon, most of the pentose is synthesized from hexose by transketolase and transaldolase. When cells adapted to grow on acetate are transferred to media containing only glucose as carbon source, the transketolase -transaldolase sequence continues to dominate during the resting phase. During logarithmic growth on glucose the oxidative decarboxylation of 6-phosphogluconate becomes more important than the transketolase -transaldolase pathway. When cells adapted to grow on acetate are repeatedly transferred on media with glucose as the sole source of carbon, four-fifths of the pentose is synthesized by oxidative decarboxylation of 6-phosphogluconate.