Abstract
The kinetics of citrate transport by induced cells of Aerobacter aerogenes was measured and an apparent K m of 2.5 × 10 −6 was determined. Citrate was transported optimally at pH 7 and 30–37 °. Osmotic shock decreased total citrate uptake by 75% but the initial rate of transport was unaffected. Shocked cells incubated with citrate recovered their ability to take up citrate, but chloramphenicol prevented this recovery. Aconitase activity was 20-fold higher in extracts from citrate-grown cells of A. aerogenes than from glucose-grown cells. Aconitase activity was diminished by osmotic shock. Aconitase activity was recovered by incubation of shocked cells with citrate concomitant with the recovery of citrate uptake. There was no accumulation of label from uptake of [6- 14C]citrate and 14CO 2 was evolved immediately. Intracellular citrate could not be detected after a 10-sec pulse with [1,5- 14C]citrate or [2,4- 14C]citrate; instead, the major intracellular product was glutamate. Citrate lyase was not detected in cell-free extracts of citrate-grown cells. These results indicated that A. aerogenes metabolized citrate as rapidly as it entered the cells and that aerobic citrate catabolism proceeded via the tricarboxylic acid cycle.
Published Version
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