Аннотация:This treatise focuses on the mechanistic aspects of the transport reaction of membrane pyrophosphatases, namely, the coupling step, the role of the chemically produced proton, subunit cooperation, and the relationship between the proton and sodium ion transport. The available data identify membrane pyrophosphatases as the first non-oxidoreductase pump with a “direct-coupling” mechanism, i.e., the transported proton is produced in the coupled chemical reaction. They also support a “billiard” hypothesis, which unifies the H+ and Na+ transport mechanisms in mPPase and, probably, other transporters.