Characterization of enzymes involved in the central metabolism of Gluconobacter oxydans |
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Authors: | Bernadette Rauch Jennifer Pahlke Paul Schweiger Uwe Deppenmeier |
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Institution: | (1) Institute fur Mikrobiologie und Biotechnologie, Universitat Bonn, 168 Meckenheimer Allee, 53515 Bonn, Germany; |
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Abstract: | Gluconobacter oxydans is an industrially important bacterium that lacks a complete Embden–Meyerhof pathway (glycolysis). The organism instead uses
the pentose phosphate pathway to oxidize sugars and their phosphorylated intermediates. However, the lack of glycolysis limits
the amount of NADH as electron donor for electron transport phosphorylation. It has been suggested that the pentose phosphate
pathway contributes to NADH production. Six enzymes predicted to play central roles in intracellular glucose and gluconate
flux were heterologously overproduced in Escherichia coli and characterized to investigate the intracellular flow of glucose and gluconates into the pentose phosphate pathway and
to explore the contribution of the pentose phosphate pathway to NADH generation. The key pentose phosphate enzymes glucose
6-phosphate dehydrogenase (Gox0145) and 6-phosphogluconate dehydrogenase (Gox1705) had dual cofactor specificities but were
physiologically NADP- and NAD-dependent, respectively. Putative glucose dehydrogenase (Gox2015) was NADP-dependent and exhibited
a preference for mannose over glucose, whereas a 2-ketogluconate reductase (Gox0417) displayed dual cofactor specificity for
NAD(P)H. Furthermore, a putative gluconokinase and a putative glucokinase were identified. The gluconokinase displayed high
activities with gluconate and is thought to shuttle intracellular gluconate into the pentose phosphate pathway. A model for
the trafficking of glucose and gluconates into the pentose phosphate pathway and its role in NADH generation is presented.
The role of NADPH in chemiosmotic energy conservation is also discussed. |
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