In enzymology, an undecaprenyl-diphosphatase (EC 3.6.1.27) is an enzyme that catalyzes the chemical reaction

undecaprenyl diphosphate + H₂O ${\displaystyle \rightleftharpoons }$ undecaprenyl phosphate + phosphate

Thus, the two substrates of this enzyme are undecaprenyl diphosphate and H₂O, whereas its two products are undecaprenyl phosphate and phosphate. The enzymatic activity is enhanced by divalent cations, particularly Ca²⁺.

In many bacteria, this enzyme is a membrane protein that participates in peptidoglycan biosynthesis. The enzyme has been implicated in conferring resistance to the antibiotic bacitracin.^[1]

This enzyme belongs to the family of hydrolases, specifically those acting on acid anhydrides in phosphorus-containing anhydrides. The systematic name of this enzyme class is undecaprenyl-diphosphate phosphohydrolase. Other names in common use include Undecaprenyl-pyrophosphate phosphatase (Uppp), UPP phosphatase, BacA, C55-isoprenyl diphosphatase, C55-isoprenyl pyrophosphatase, and isoprenyl pyrophosphatase.^[2]

Note: The enzyme Uppp/BacA (EC 3.6.1.27) has occasionally been incorrectly termed an "undecaprenol kinase".^[3] However, that name should be reserved for a distinct enzyme (EC 2.7.1.66), which catalyses the addition of a phosphate group from ATP to undecaprenol (C55-isoprenyl alcohol).

X-ray crystal structures of the membrane-form of the enzyme from E. coli^[4][5] are available (PDB IDs: 5OON,^[6] 6CB2^[7]).