Membrane‐Bound Pyrophosphatases

Abstract

Membrane‐bound pyrophosphatases (M‐PPases) are homodimeric enzymes that couple the vectorial transport of protons and/or sodium ions to pyrophosphate (PP i ) hydrolysis or synthesis. They are found in prokaryotes, plants, and protists and are thus present in all three domains of life. M‐PPases have an important role in conferring tolerance against abiotic stress conditions and are also vital for plant maturation. Like many proteins that catalyze the formation or cleavage of phosphoanhydride bonds (e.g., P‐ and F‐type ATPases, soluble PPases), M‐PPases require magnesium for activity, both because they bind 2–3 free Mg 2+ ions and because the catalytically relevant substrate at physiological pH and Mg ion concentration is Mg 2 PP i . Besides this alkaline earth metal, M‐PPases also bind alkali metals: Na + ‐pumping M‐PPases bind and transport Na + and certain M‐PPases bind and are activated by K + . In this article, we give a concise summary of the current structural and functional understanding of M‐PPases, with an emphasis on describing the role of the metal ions in the enzymatic function of these proteins.