The oxaloacetate decarboxylase primary Na+ pump (Oad) produces energy for the surviving of some pathogenic bacteria under anaerobic conditions. Oad composes of three subunits: Oad-alpha, a biotinylated soluble subunit and catalyzes the decarboxylation of oxaloacetate; Oad-beta, a transmembrane subunit and functions as a Na+ pump; and Oad-gamma, a single transmembrane alpha-helical anchor subunit and assembles Oad-alpha/beta/gamma complex. The molecular mechanism of Oad complex coupling the exothermic decarboxylation to generate the Na+ electrochemical gradient remains unsolved. Our biophysical and biochemical studies suggested that the stoichiometry of Oad complex from Vibrio cholerae composed of alpha, beta, gamma in 4:2:2 stoichiometry not that of 4:4:4. The high-resolution structure determination of the Oad complex would reveal the energetic transformation mechanism from the catalytical soluble alpha subunit to membrane beta subunit. Sufficient amount stable, conformational homogenous and active Oad complex with the right stoichiometry is the prerequisite for structural analysis. Here we report an easy and reproducible protocol to obtain high quantity and quality Oad complex protein for structural analysis. (C) 2015 Elsevier Inc. All rights reserved.