6533b828fe1ef96bd1288e07

RESEARCH PRODUCT

Requirement for the Proton-Pumping NADH Dehydrogenase I of Escherichia Coli in Respiration of NADH to Fumarate and Its Bioenergetic Implications

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description

In Escherichia coli the expression of the nuo genes encoding the proton pumping NADH dehydrogenase I is stimulated by the presence of fumarate during anaerobic respiration. The regulatory sites required for the induction by fumarate, nitrate and O2 are located at positions around –309, –277, and downstream of –231 bp, respectively, relative to the transcriptional-start site. The fumarate regulator has to be different from the O2 and nitrate regulators ArcA and NarL. For growth by fumarate respiration, the presence of NADH dehydrogenase I was essential, in contrast to aerobic or nitrate respiration which used preferentially NADH dehydrogenase II. The electron transport from NADH to fumarate strongly decreased in a mutant lacking NADH dehydrogenase I. The mutant used acetyl-CoA instead of fumarate to an increased extent as an electron acceptor for NADH, and excreted ethanol. Therefore, NADH dehydrogenase I is essential for NADH → fumarate respiration, and is able to use menaquinone as an electron acceptor. NADH → dimethylsulfoxide respiration is also dependent on NADH dehydrogenase I. The consequences for energy conservation by anaerobic respiration with NADH as a donor are discussed.