title: 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.
authors.affiliation: Institute of Biotechnology 2, Forschungszentrum Jülich, Jülich 52425, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Bartek
authors.forename: Bastian
authors.initials: B
authors.lastname: Blombach
authors.forename: Enrico
authors.initials: E
authors.lastname: Zönnchen
authors.forename: Pia
authors.initials: P
authors.lastname: Makus
authors.forename: Siegmund
authors.initials: S
authors.lastname: Lang
authors.forename: Bernhard J
authors.initials: BJ
authors.lastname: Eikmanns
authors.forename: Marco
authors.initials: M
authors.lastname: Oldiges
mesh_terms: D018929:Cell Culture Techniques; D048230:Corynebacterium glutamicum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D003470:Culture Media; D005285:Fermentation; D005956:Glucose-6-Phosphate Isomerase / Q000235:genetics; D053858:Metabolic Networks and Pathways; D055442:Metabolome; D008954:Models, Biological; D009249:NADP / Q000378:metabolism*; D014633:Valine / Q000378:metabolism*
chemical_list: D003470:Culture Media; D009249:NADP; D005956:Glucose-6-Phosphate Isomerase; D014633:Valine