In enzymology, a guanosine-5'-triphosphate,3'-diphosphate diphosphatase () is an enzyme that catalyzes the chemical reaction.
Thus, the two substrates of this enzyme are guanosine 5'-triphosphate,3'-diphosphate and H<sub>2</sub>O, whereas its two products are guanosine 5'-diphosphate,3'-diphosphate and phosphate.
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 guanosine-5'-triphosphate,3'-diphosphate 5'-phosphohydrolase. Other names in common use include pppGpp 5'-phosphohydrolase, guanosine-5'-triphosphate,3'-diphosphate pyrophosphatase, guanosine 5'-triphosphate-3'-diphosphate 5'-phosphohydrolase, guanosine pentaphosphatase, guanosine pentaphosphate phosphatase, guanosine 5'-triphosphate 3'-diphosphate 5'-phosphatase, and guanosine pentaphosphate phosphohydrolase. This enzyme participates in purine metabolism.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes and .