ACTIVATION OF CHLOROPLAST FRUCTOSE-1,6-BISPHOSPHATASE OF PISUM-SATIVUM BY MOLE MASS CHANGE

Separation of extracts, obtained from isolated intact P.sativum chloro plasts, by fast protein liquid chromatography (FPLC) on superose 6, re veals a 1,400 kDa-FBPase II form at pH 6.0 and a 380 kDa form at pH 7. 5. Addition of F1,6 P-2, Mg++ and ATP cause dissociation of the large form into the smaller one, which leads to an approximate 4-fold increa se in activity. Reversibility of the mole mass change could be shown f or the influence of pH and of fructose-1,6-bisphosphate on purified en zyme samples, separated from crude leaf extracts. Compared to the larg e enzyme form, the small form has higher activity and is specific for the substrate fructose-1,6-bisphosphate, while the large form is not. Activation of FBPase II in the light and inactivation in the dark is d iscussed on the basis of different oligomeric forms of the enzyme caus ed by changes in the concentration of intermediates and effecters in t he chloroplast stroma. The conclusion is drawn that oligomerization of key enzymes might provide an effective mechanism for enzyme activatio n/inactivation in vivo.