Coupling of energy to active transport of amino acids in Escherichia coli.

Active transport of amino acids in isolated membrane vesicles of E. coli ML 308-225 is stimulated by oxidation of D-lactate, and this stimulation is dependent on electron transport [Kaback, H. R. & Milner, L. S. (1970) Proc. Nat. Acad. Sci. USA 66, 1008]. In attempting to relate these results to amino-acid transport in intact cells, we isolated mutants of E. coli ML 308-225 that contain defects in D-lactate dehydrogenase (EC 1.1.2.4) and electron transport. Intact cells of these mutants are normal for transport of proline and alanine. We also isolated mutants defective in Ca,Mg-stimulated ATPase (EC 3.6.1.3), which is responsible for coupling electron transport to the synthesis of ATP. These mutants are defective in their ability to transport proline and alanine, as measured both in cells and isolated membrane vesicles. A possible role for the ATPase in coupling energy to active transport is discussed.