Reconstitution of sodium transport from purified oxaloacetate decarboxylase and phospholipid vesicles.

The Na+-pumping oxaloacetate decarboxylase, isolated from Klebsiella aerogenes membranes, was incorporated into the membranes of lecithin liposomes. Reconstitution of Na+ transport in this artificial system was achieved by the detergent dilution method with octylglucoside as the detergent. An optimum Na+ transport activity upon dilution was obtained in the presence of about 2.7% octylglucoside. With these reconstituted vesicles, a steady state internal Na+ concentration was established by oxaloacetate decarboxylation which was about 30 times higher than that of the external medium. The presence of low concentrations of the Na+-carrying ionophores nigericin or trinactin almost completely abolished the oxaloacetate-dependent Na+ transport, whereas the uncoupler, carbonylcyanide-p-trifluoromethoxyphenylhydrazone, was without effect. The results are in accord with the function of oxaloacetate decarboxylase as a primary active Na+ pump converting the energy of the decarboxylation reaction into a Na+ gradient.