Zn2+‐Dependent Acid Inorganic Pyrophosphatase Activity as Related to Other Pyrophosphatases in Oryza sativa

Abstract Acid inorganic pyrophosphatase on the one hand, and Mg2+‐dependent alkaline inorganic pyrophosphatase and Zn2+‐dependent acid inorganic pyrophosphatase on the other hand showed opposite trends in their activities in rice (Oryza sativa L. cv. Ratna) seedlings grown in dark and sun. The opposite trends in their activities were also noted in rice seedlings grown from gamma‐irradiated seeds and in detached rice leaves floated on water in dark. The ratios of Mg2+ dependent alkaline inorganic pyrophosphatase/acid inorganic pyrophosphatase and Zn2+‐dependent acid inorganic pyrophosphatase/acid inorganic pyrophosphatase changed significantly in response to the above physical treatments, but the ratio of Mg2+ dependent alkaline inorganic pyrophosphatase/Zn2+ dependent acid inorganic pyrophosphatase remained relatively stable. The conclusion is that Zn2+‐dependent acid inorganic pyrophosphatase activity is the same as that of Mg2+‐dependent alkaline inorganic pyrophosphatase and is different from that of acid inorganic pyrophosphatase, which requires no metal ion for activity. The acid and alkaline inorganic pyrophosphatase activities are due to separate enzyme proteins.