The effect of divalent metal ions on the activity of Mg(++) depleted ribulose-1,5-bisphosphate oxygenase.

Ribulose-1,5-bisphosphate carboxylase-oxygenase is deactivated by removal of Mg(++). The enzyme activities can be restored to a different extent by the addition of various divalent ions in the presence of CO2. Incubation with Mg(++) and CO2 restores both enzyme activities, whereas, the treatment of the enzyme with the transition metal ions (Mn(++), Co(++), and Ni(++)) and CO2 fully reactivates the oxygenase: however, the carboxylase activity remains low. In experiments where CO2-free conditions were conscientiously maintained, no reactivation of RuBP oxygenase was observed, although Mn(++) ions were present. Other divalent cations such as Ca(++) and Zn(++), restore neither the carboxylase nor the oxygenase reaction. Furthermore, the addition of Mn(++) to the Mg(++) and CO2 preactivated enzyme significantly inhibited carboxylase reactions, but increased the oxygenase reaction.