Purification and properties of a chloroplastic phosphatase distinct from fructose bisphosphatase

A chloroplast phosphatase, distinct from fructose bisphosphatase, has been isolated and purified to apparent electrophoretic homogeneity from spinach leaves. This 100-kDa enzyme hydrolyzes both fructose and sedoheptulose bisphosphates. Given this lack of absolute substrate specificity, it cannot be considered a typical sedoheptulose bisphosphatase. The enzyme is reductively activated by reduced thioredoxin f_B in the presence of dithiothreitol (DTT), but not by thioredoxin f_A or thioredoxin m. Oxidized thioredoxin f_B deactivates the active reduced phosphatase.