GENETICS OF PENTOSE-PHOSPHATE PATHWAY ENZYMES OF ESCHERICHIA-COLI K-12

The pentose-phosphate pathway of Escherichia coli K-12, in addition to its role as a route for the breakdown of sugars such as glucose or pe ntoses, provides the cell with intermediates for the anabolism of amin o acids, vitamins, nucleotides, and cell wall constituents. Through it s oxidative branch, it is a major source of NADPH. The expression of t he gene for NADP-dependent 6-phosphogluconate dehydrogenase (gnd) is r egulated by the growth rate in E. coil. The recently identified gene f or ribulose-5-phosphate 3-epimerase (rpe) is part of a large operon th at comprises among others genes for the biosynthesis of aromatic amino acids. In recent years, genes for all enzymes of the pathway have bee n cloned and sequenced. Isoenzymes have been found for transketolase ( genes tktA and tktB), ribose-5-phosphate isomerase (rpiA and rpiB) and transaldolase (talA and talB).