Importance of NADPH supply for improved L‐valine formation in Corynebacterium glutamicum

Abstract

Cofactor recycling is known to be crucial for amino acid synthesis. Hence, cofactor supply was now analyzed for L-valine to identify new targets for an improvement of production. The central carbon metabolism was analyzed by stoichiometric modeling to estimate the influence of cofactors and to quantify the theoretical yield of L-valine on glucose. Three different optimal routes for L-valine biosynthesis were identified by elementary mode (EM) analysis. The modes differed mainly in the manner of NADPH regeneration, substantiating that the cofactor supply may be crucial for efficient L-valine production. Although the isocitrate dehydrogenase as an NADPH source within the tricarboxylic acid cycle only enables an L-valine yield of Y(Val/Glc) = 0.5 mol L-valine/mol glucose (mol Val/mol Glc), the pentose phosphate pathway seems to be the most promising NADPH source. Based on the theoretical calculation of EMs, the gene encoding phosphoglucoisomerase (PGI) was deleted to achieve this EM with a theoretical yield Y(Val/Glc) = 0.86 mol Val/mol Glc during the production phase. The intracellular NADPH concentration was significantly increased in the PGI-deficient mutant. L-Valine yield increased from 0.49 +/- 0.13 to 0.67 +/- 0.03 mol Val/mol Glc, and, concomitantly, the formation of by-products such as pyruvate was reduced.

Improvement of NADPH bioavailability in Escherichia coli through the use of phosphofructokinase deficient strains

“…1). Strategies such as overexpression of zwf, encoding glucose-6-phosphate dehydrogenase (G6PDH) (Chin et al 2009;Kim et al 2011b;Lee et al 2007), or deletion of pgi, encoding phosphoglucose isomerase (Bartek et al 2010;Chemler et al 2010;Kim et al 2011a), have been used to increase the metabolic flux to PPP from glycolysis. Other strategies include overexpression of pyridine nucleotide transhydrogenase encoded by udhA which converts NADH to NADPH (Sanchez et al 2006), and switching the glycolytic enzyme, NAD + dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to NADP + -dependent GAPDH from Clostridium acetobutylicum (Martinez et al 2008).…”

Speciation of Binary Complexes of Pb(II), Cd(II) and Hg(II) with L-Valine in Low Dielectric Media

“…It has wide applications in the field of pharmaceutical and food industry 15 . It is a bidentate ligand and formation of its binary complexes of with metals was reported earlier, using polrographic study 16 , batch equilibrium method with cation exchange resin 17 , potentiometric titration method 18 and pH metric titration method 19 .…”

Speciation studies of Co(II), Ni(II) and Cu(II) complexes of L-valine in acetonitrile–water mixtures

“…Lack of L-valine may influence the growth of body, cause neuropathic obstacle and anemia. It has many applications in the pharmaceutical industry (Bartek et al, 2010). Binary stability constants of L-valine with Co(II), Ni(II) and Cu(II) have been reported using batch equilibrium method with cation exchange resin (Hirano and Koyanagi, 1981), and potentiometric (Albert, 1950) and pH-metric (Rengaraj et al, 1991) titration methods.…”