Isolation of the soluble substrate recognition component of the dicarboxylate transport system of Escherichia coli.

A soluble, periplasmic protein was isolated from Escherichia coli cells by chromatography on columns of aspartate-coupled Sepharose 4B. This protein has a molecular weight of about 15,000 and, as judged by competition experiments, binds the three dicarboxylic acids, succinate, malate, and fumarate and, addition, the monocarboxylic acid D-lactate. The periplasmic protein seems to be missing from some mutants of E. coli (designated cbt) which are incapable of transporting succinate in whole cells.