Abstract
Mutants of E. coli which lack the activity of NAD-specific malate dehydrogenase show the presence of a FAD-dependent malate oxidase which can be assayed using ferricyanide as an electron acceptor. Cells which acquire the ability to form malate dehydrogenase cease to produce detectable levels of malate oxidase. Activity of malate dehydrogenase is definitely required to suppress synthesis of malate oxidase. The substrate and product of malate dehydrogenase, L-malate and oxalacetate, respectively, are apparently not involved in the regulation of malate oxidase. Presence of high derepressed levels of malate oxidase in malate dehydrogenase deficient mutants are determined by a gene linked closely to argG locus. Malate oxidase is produced in small amounts in minimal-glucose medium, but in high concentrations in complex medium. The peak levels are reached in early log phase of growth after which there is a dramatic drop with the approach of stationary phase.
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