Unexpected specificity in the thioredoxin activation of fructose-bis-phosphatases from different plants

Green seedlings of soy bean and wheat contain, like the plant seeds, multiple thioredoxin proteins which possess all typical thioredoxin properties but are inactive in the stimulation assay with spinach fructose-bis-phosphatase. However the pure proteins do have thioredoxin f activity when tested with homologous enzymes isolated from soy bean or wheat leaves, respectively, in the presence of Mg++. This new type of species specificity, unknown in all other in vitro assays of reduced thioredoxins, has to be considered in characterizing complete thioredoxin profiles in plants.