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Journal of Bacteriology, December 2000, p. 6884-6891, Vol. 182, No. 24
Biotechnologisches Zentrallabor, Geb. 25.12, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
Received 17 May 2000/Accepted 21 September 2000
Like many other bacteria, Corynebacterium glutamicum
possesses two types of L-malate dehydrogenase, a
membrane-associated malate:quinone oxidoreductase (MQO; EC 1.1.99.16)
and a cytoplasmic malate dehydrogenase (MDH; EC 1.1.1.37) The
regulation of MDH and of the three membrane-associated dehydrogenases
MQO, succinate dehydrogenase (SDH), and NADH dehydrogenase was
investigated. MQO, MDH, and SDH activities are regulated coordinately
in response to the carbon and energy source for growth. Compared to
growth on glucose, these activities are increased during growth on
lactate, pyruvate, or acetate, substrates which require high citric
acid cycle activity to sustain growth. The simultaneous presence of high activities of both malate dehydrogenases is puzzling. MQO is the
most important malate dehydrogenase in the physiology of C. glutamicum. A mutant with a site-directed deletion in the
mqo gene does not grow on minimal medium. Growth can be
partially restored in this mutant by addition of the vitamin
nicotinamide. In contrast, a double mutant lacking MQO and MDH does not
grow even in the presence of nicotinamide. Apparently, MDH is able to
take over the function of MQO in an mqo mutant, but this
requires the presence of nicotinamide in the growth medium. It is shown that addition of nicotinamide leads to a higher intracellular pyridine
nucleotide concentration, which probably enables MDH to catalyze malate
oxidation. Purified MDH from C. glutamicum catalyzes
oxaloacetate reduction much more readily than malate oxidation at
physiological pH. In a reconstituted system with isolated membranes and
purified MDH, MQO and MDH catalyze the cyclic conversion of malate and
oxaloacetate, leading to a net oxidation of NADH. Evidence is presented
that this cyclic reaction also takes place in vivo. As yet, no
phenotype of an mdh deletion alone was observed, which
leaves a physiological function for MDH in C. glutamicum obscure.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Functions of the Membrane-Associated and Cytoplasmic Malate
Dehydrogenases in the Citric Acid Cycle of Corynebacterium
glutamicum
*
Corresponding author. Mailing address:
Biotechnologisches Zentrallabor, Geb. 25.12, Heinrich-Heine-Universität, Universitätsstraße 1, D-40225
Düsseldorf, Germany. Phone: 49 211 811 1482. Fax: 49 211 811 5370. E-mail: molenaar{at}rz.uni-duesseldorf.de.
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