The effect of inorganic fluoride on the reactions catalyzed by ribulosebisphosphate carboxylase/oxygenase has been characterized with the fully activated enzyme. Fluoride inhibits both reactions, and the concentration required to inhibit the activity of the magnesium-activated enzyme 50% is 2 mM when reactions are carried out at pH 8.3. Inhibition is strongly pH dependent with an apparent pKa of 8.8. The inhibition kinetics were studied. It was found that inhibition is mixed but close to noncompetitive with respect to CO2 and uncompetitive with respect to ribulose 1,5-bisphosphate. The mechanism of interaction between fluoride and the enzyme is discussed, and a model is proposed in which fluoride interferes with the reactions by displacing a catalytically important ligand, probably a water molecule, from the activator metal.
Carboxy-Lyases Cobalt