Stimulation of spinach (Spinacia oleracea) chloroplast fructose-1,6-bisphosphatase by mercuric ions

Chloroplast fructose-1,6-bisphosphatase can exist in an active reduced form or a less active oxidised form. Oxidised fructose bisphosphatase from spinach (Spinacia oleracea) could be stimulated up to many hundred-fold by 0.1 mM HgCl2 whereas fructose bisphosphatases from rabbit, yeast, a non-chloroplast enzyme from spinach and the reduced chloroplast enzyme were only inhibited by HgCl2. Stimulation of the enzyme was maximal at pH 8.0 and low magnesium concentrations where the oxidised enzyme normally has little activity.