A CYTOCHROME THAT CAN PUMP SODIUM-ION

Previous studies have shown that the bacterium, Vitreoscilla, generates a respiratory-driven ΔψNa+. Two major respiratory electron transport proteins, NADH dehydrogenase (NADH:Quinone oxidoreductase), and cytochrome o terminal oxidase are candidates for the electrogenic Na+ pumping that mediates the ΔψNa+ formation. The NADH oxidase activity of the membranes was enhanced more by Na+ than by Li+. The NADH:Quinone oxidoreductase activity in the respiratory chain was enhanced by Na+ and Li+, whereas the quinol oxidase activity of cytochrome o was enhanced specifically by Na+, and not by Li+, K+, or choline. Purified cytochrome o, reconstituted into Na+-loaded liposomes in the right-side-out orientation, catalyzed a net Na+ extrusion when energized with Q1H2 1. In non-loaded inside-out proteoliposomes, this cytochrome catalyzed a net uptake of 22Na+ when energized with ascorbate/TMPD. Both Na+-pumping activities were inhibited by CN-. These results are consistent with the Vitreoscilla cytochrome o being a redox-driven Na+ pump. © 1990 Academic Press, Inc.