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 chloropla st ATPase have been compared, using an HPLC method for the separation of AD P. The dissociation constants of the divalent ion-ATP complexes have been d etermined by a spectrophotometric method, with the dye antipyrylazo III, an d enzymic constants (dissociation constant of the ion-enzyme complexes, Mic haelis constants, maximum rates) have been calculated. The comparison betwe en the rates obtained, respectively, with Mn2+ and Ca2+ alone with that giv en 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.