Comparison of different cations (Mn2+, Mg2+, Ca2+) on the hydrolytic activity of chloroplast ATPase.

The influences of Mn2+, Mg2+, and Ca2+ on the enzymic activity of chloroplast ATPase have been compared, using an HPLC method for the separation of ADP. The dissociation constants of the divalent ion-ATP complexes have been determined by a spectrophotometric method, with the dye antipyrylazo III, and enzymic constants (dissociation constant of the ion-enzyme complexes, Michaelis constants, maximum rates) have been calculated. The comparison between the rates obtained, respectively, with Mn2+ and Ca2+ alone with that given by the mixture of these two ions, allows us to conclude that, as for Mg2+, Mn2+ is also an activator of chloroplast ATPase and that metal-free ATP is the true substrate.