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 h ydroxyl 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 prepare d from the plant Vigna radiata. The inhibition constant for aminomethy lenediphosphonate, which binds competitively with respect to substrate , is below 2 muM. Rat liver mitochondrial pyrophosphatase is two order s of magnitude less sensitive to this compound but extremely sensitive to imidodiphosphate. By contrast, fluoride is highly effective only a gainst the mitochondrial pyrophosphatase. It is concluded that the mit ochondrial pyrophosphatase and the H+-pyrophosphatases of chromatophor es and vacuolar membranes belong to two different classes of enzyme.