The Uptake of C₄‐Dicarboxylic Acids by <i>Escherichia coli</i>

Abstract

Escherichia coli inducibly form a system effecting the uptake of a number of C 4 ‐dicarboxylic acids; glucose or inhibitors of protein synthesis prevent this induction. After growth on C 4 ‐dicarboxylic acids; glucose or inhibitors of protein synthesis prevent this induction. After growth onC 4 ‐dicarboxylic acids, washed cells take up such acids rapidly and, initially, linearly with time; the K m for this process is approx. 30 μM and the V max is approx. 25 nmoles X min −1 mg dry wt −1 , irrespective of the identity of the acid transported. C 4 ‐dicarboxylic acids other than fumarate, succinate, malate, aspartate, and maleate, are takep up poorly. Washed cells talking up 14 C‐labelled C 4 ‐dicasrboxylic acids incorporate isotope mainly into macromolecular cell components; no significant intracellular accumulation of C 4 ‐acids is observed. Mutants blocked in component reactions of the tricarboxylic acid cycle are also greatly impaired in their ability to take up C 4 ‐acids; mutants blocked in reaction ancillary to the cycle are not. It is suggested that E. coli effect the uptake of C 4 ‐dicarboxylic acids througha common, inducible and highly specific transport system.