Changes of pentose phosphate pathway flux in vivo in Corynebacterium glutamicum during leucine-limited batch cultivation as determined from intracellular metabolite concentration measurements

Corynebacterium glutamicum is an important organism for the industrial production of amino acids such as lysine. In the present study time-dependent changes in the oxidative pentose phosphate pathway activity, an important site of NADPH regeneration in C. glutamicum, are investigated, whereby intracellular metabolite concentrations and specific enzyme activities in two isogenic leucine auxotrophic strains differing only in the regulation of their aspartate kinases were compared. After leucine limitation only the strain with a feedback-resistant aspartate kinase began to excrete lysine into the culture medium. Concomitantly, the intracellular NADPH to NADP concentration ratio increased from 2 to 4 in the non-producing strain, whereas it remained constant at about 1.2 in the lysine-producing strain. From these data the in'vivo flux through the pentose phosphate pathway was calculated. These results were used to approximate the total NADPH regeneration by glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase, which agreed fairly well with the calculated demands for biomass formation and lysine biosynthesis. The analysis allowed to conclude that NADPH regeneration in the pentose phosphate pathway is essential for lysine biosynthesis in C. glutamicum.