Control of synthesis of malate dehydrogenase in Aerobacter aerogenes.

An inverse linear relationship was observed between the levels of l-malate dehydrogenase (MDH) and growth rates of Aerobacter aerogenes when grown under aerobic and anaerobic conditions on various substrates which served as the sole carbon and energy sources. Deviations from this linearity were found. MDH levels of cells grown aerobically on oxalacetate, l-malate, d-mannose and d-galactose, and of cells grown anaerobically on l-malate and d-mannose were higher than those expected according to this relationship. Enzyme levels of cells grown aerobically on maltose, d-glucuronate, pyruvate, and possibly melibiose and sucrose were lower than the expected ones. Experiments in which the cells were grown on a mixture of two substrates showed that substrates which gave low levels of MDH repressed the synthesis of this enzyme even in the presence of l-malate or other "high-level substrates." Repressed levels were also observed when the mixture contained l-malate together with "intermediate" or high-level substrates. Identical MDH patterns were obtained by acrylamide gel electrophoresis for all the enzymatic preparations.