Membrane-bound potassium and magnesium ion-stimulated inorganic pyrophosphatase from roots and cotyledons of sugar beet (Beta vulgaris L).

1. The 25 000-30 000 X g fraction from sugar beet leaf or roots contains, together with (Na+ plus K+)-activated ATPase, also K+-stimulated inorganic pyrophosphatase. 2. This inorganic pyrophosphatase is also stimulated by Rb+ and to a lesser degree by Li+ and Na+. 3. Na+ is at the same time an inhibitor to the K+-stimulation of the inorganic pyrophosphatase. 4. No signs of synergism for (Na+ plus K+) were found. 5. Optimum pH was at about 8.5.