Hpyrophosphatase

Hpyrophosphatase, commonly referred to as H+-pyrophosphatase or H+-PPase, is a membrane-bound enzyme that catalyzes the hydrolysis of inorganic pyrophosphate (PPi) to two inorganic phosphate (Pi) molecules. The exergonic reaction is coupled to the translocation of protons (H+) across membranes, generating or augmenting a proton motive force used for secondary transport and membrane energization. The enzyme is categorized as a pyrophosphatase and is distinct from soluble inorganic pyrophosphatases.

Biochemically, H+-PPase requires divalent cations, typically Mg2+, for catalytic activity. It proceeds with PPi hydrolysis and uses the released energy to pump protons across the membrane, often into vacuolar or endomembrane compartments in plants and into the plasma membrane in some bacteria. The protein is a multi-pass transmembrane molecule with a catalytic core that binds PPi and coordinates metal ions; several conserved regions contribute to substrate binding and proton translocation.

H+-PPases are found across bacteria, archaea, plants, and some algae. In plants, they localize to the vacuolar (tonoplast) membrane and play roles in vacuolar acidification, osmoregulation, and cellular pH homeostasis. In bacteria, they contribute to energy balance and may support various transport processes. Animals generally lack conventional H+-PPases, relying instead on other proton-transport systems such as V-ATPases.

In plants, a well-studied example is the AVP1 gene of Arabidopsis thaliana, encoding a vacuolar H+-PPase. Overexpression can enhance drought tolerance and biomass in some crops, highlighting potential biotechnological applications while underscoring the enzyme’s role in plant physiology and stress responses.