H+‐proton‐pumping inorganic pyrophosphatase: a tightly membrane‐bound family

Abstract

The earliest known H⁺‐proton‐pumping inorganic pyrophosphatase, the integrally membrane‐bound H⁺‐proton‐pumping inorganic pyrophosphate synthase from Rhodospirillum rubrum, is still the only alternative to H⁺‐ATP synthase in biological electron transport phosphorylation. Cloning of several higher plant vacuolar H⁺‐proton‐pumping inorganic pyrophosphatase genes has led to the recognition that the corresponding proteins form a family of extremely similar proton‐pumping enzymes. The bacterial H⁺‐proton‐pumping inorganic pyrophosphate synthase and two algal vacuolar H⁺‐proton‐pumping inorganic pyrophosphatases are homologous with this family, as deduced from their cloned genes. The prokaryotic and algal homologues differ more than the H⁺‐proton‐pumping inorganic pyrophosphatases from higher plants, facilitating recognition of functionally significant entities. Primary structures of H⁺‐proton‐pumping inorganic pyrophosphatases are reviewed and compared with H⁺‐ATPases and soluble proton‐pumping inorganic pyrophosphatases.