= Inorganic diphosphatase
<Inorganic diphosphatase> catalyses <diphosphate> <hydrolysis>, producing two <phosphate> products per substrate molecule. Its classification is EC 3.6.1.1. Substrate specificity and activation by metal ions depend on the source of the enzyme.<Enzyme Nomenclature by the IUBMB>[EC 3.6.1.1, Reaction and Comments]{ref}
An explicitly balanced representation for chosen ionic forms is
$$
\mathrm{P_2O_7^{4-}+H_2O\longrightarrow2HPO_4^{2-}}.
$$
Both sides contain two phosphorus atoms, eight oxygens, two hydrogens and net charge $-4$. If the substrate is instead $\mathrm{HP_2O_7^{3-}}$, an additional proton appears on the product side. These balances specify forms without asserting which dominates at an unspecified pH.
A constructed assay gives a practical consequence of the two-to-one product ratio. If measured phosphate increases by $12\,\mathrm{nmol}$ while the matched blank increases by $2\,\mathrm{nmol}$, the net signal is 10 nmol phosphate, corresponding to 5 nmol diphosphate hydrolysed, provided no other reaction contributes.
In 1952, <M. Kunitz> isolated a crystalline yeast enzyme and characterized phosphate production, metal activation and reaction-condition dependence.<Crystalline inorganic pyrophosphatase isolated from baker's yeast by M. Kunitz>[Abstract, crystalline enzyme and catalytic properties]{ref} The experiment ties a purified protein preparation to a measured chemical reaction. Crystallinity alone would not supply that activity assignment, and its properties do not automatically describe every soluble or membrane-associated diphosphatase.
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