This membrane-associated enzyme is an alternative to the better-known NAD-dependent malate dehydrogenase as part of the TCA cycle. The reduction of a quinone rather than NAD+ makes the reaction essentially irreversible in the direction of malate oxidation to oxaloacetate. Both forms of malate dehydrogenase are active in E. coli; disruption of this form causes less phenotypic change. In some bacteria, this form is the only or the more important malate dehydrogenase. [Energy metabolism, TCA cycle]
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