Transient pH changes during D-lactate oxidation by membrane vesicles

Abstract

Membrane vesicles from Escherichia coli B/r were incubated anaerobically in the presence of 10 mM D-lactate. Addition of a small quantity of an air-saturated KC1 solution resulted in a rapid drop in pH followed by a gradual return to the original value. No pH changes were seen when anaerobic KC1 was added, or when air-saturated KC1 was added in the absence of D-lactate. Electron transport inhibitors and uncouplers attenuated the pH changes. The pH changes may result from the formation of a transmembrane hydrogen ion gradient during D-lactate oxidation.