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l,l-Diphosphonate analogs of pyrophosphate, containmg an amino or a hydroxyl group on the bridge carbon atom, are potent mhibitors of the H*-translocating pyrophosphatases of chromatophores prepared from the bacterium R~udospzr~~Zut~l rubnon and vacuolar membraI~e vesicles prepared from the plant yigna vu&&z. The mhibttton constant for aminomethylenediphosphonate, which bmds competitively with respect to substrate, ts below 2 PM. Rat liver mitochondrial pyrophosphatase is two orders of magnitude less sensitive to this compound but extremely sensitive to imidodiphosphate. By contrast, fluoride is highly effective only against the mitochondrial pyrophosphatase. It 1s concluded that the mttochondrial pyrophosphatase and the H+-pyrophosphatases of ehromatophores and vacuolar membranes belong to two different classes of enzyme.

Substrate hydrolysis by the H+-pyrophosphatase (pyrophosphate phosphohydrolase, H+-PPase) of the photosynthetic bacterium Rhodospirillum rubrum follows a two-pathway reaction scheme in which preformed 1 : 1 and 1 : 2 enzyme . Mg2+ complexes (EMg and EMg2) convert dimagnesium pyrophosphate (the substrate). This scheme is applicable to isolated enzyme, uncoupled chromatophores and chromatophores energized by a K+/valinomycin diffusion potential. Tris and other amine buffers exert a specific effect on the bacterial H+-PPase by increasing the Michaelis constant for substrate binding to EMg by a factor of 26-32, while having only small effect on substrate binding to EMg,. Formation of EMg requires a basic group with pK, of 7.2-7.7 and confers resistance against inactivation by mersalyl and N-ethylmaleimide to H+-PPase. The dissociation constants governing EMg and EMg, formation, as estimated from the mersalyl-protection assays and steady-state kinetics of PP, hydrolysis, respectively, differ by an order of magnitude. Comparison with the data on soluble PPases suggests that, in spite of gross structural differences between H+-PPase and soluble PPases and the added ability of H+-PPase to act as a proton pump, the two classes of enzyme utilize the same reaction mechanism in PP, hydrolysis.

Inorganic pyrophosphatase (PPase) from E. coli was used as label in enzyme immunoassay for the detection of different plant viruses. The use of PPase‐conjugated antibodies and tetrasodium pyrophosphate as a substrate in ELISA provides some advantages in detection of plant viruses in purified preparations and extracts from plant specimens: high sensitivity, negligible level of background reactions in control samples, bright blue‐greenish colour which allows to detect the reaction visually and high stability of PPase‐conjugated antibodies.

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