Activation of spinach chloroplast fructose-1,6-bisphosphatase by monovalent cations.

Spinach chloroplast fructose 1,6-bisphosphatase, like its counterparts from animal sources, can be activated by monovalent cations such as potassium and ammonium ions. The extents of activation are closely related to the pH values and the concentrations of magnesium ions. The activation effect is most prominent when the concentrations of magnesium ions are high enough to exert inhibitory side effect on the enzyme. Similar to the cases of enzymes from mammalian tissues, activation of the chloroplast enzyme by monovalent cations is, at least partially, due to overcoming of the inhibitory effect by the excess of magnesium ions. The enzyme can also be activated by low concentrations of guanidine hydrochloride, which probably involves a similar mechanism compared with that by monovalent cations.