DIFFERENTIAL SENSITIVITY OF MEMBRANE-ASSOCIATED PYROPHOSPHATASES TO INHIBITION BY DIPHOSPHONATES AND FLUORIDE DELINEATES 2 CLASSES OF ENZYME

1,1-Diphosphonate analogs of pyrophosphate, containing an amino or a hydroxyl group on the bridge carbon atom, are potent inhibitors of the H+-translocating pyrophosphatases of chromatophores prepared from the bacterium Rhodospirillum rubrum and vacuolar membrane vesicles prepared from the plant Vigna radiata. The inhibition constant for aminomethylenediphosphonate, which binds competitively with respect to substrate, is below 2 muM. 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 is concluded that the mitochondrial pyrophosphatase and the H+-pyrophosphatases of chromatophores and vacuolar membranes belong to two different classes of enzyme.