Abstract
The activities of enzymes in the Krebs cycle and in electron transport were determined with membrane and soluble fractions of Escherichia coil cells grown aerobically or anaerobically with or without glucose. The absence of oxygen during growth decreased the levels of aconitate hydratase, isocitrate lyase, isocitrate dehydrogenase, fumarate hydratase, NADP-malate dehydrogenase, NADH-oxidase, and cytochrome b1, while the presence of glucose repressed the levels of aconitate hydratase, isocitrate lyase, fumarate hydratase, and succinate dehydrogenase. Formate dehydrogenase was repressed only when cells were grown anaerobically with glucose, while NADPH-oxidase and menadione reductase were neither repressed by glucose nor by anaerobiosis. Regardless of the cultural conditions, most of the activities of formate dehydrogenase, succinate dehydrogenase, NADH oxidase, and cytochrome b1 were found in the membrane fraction, but the proportions of the activities found in soluble fraction considerably increased when the formation of these enzymes was repressed by anaerobiosis or by glucose.
