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

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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.