FIG. 4.

Divalent cation dependency and specificity. (A) Reaction mixtures (10 μl) containing 50 mM Tris-HCl (pH 7.5), 0.2 mM [γ-³²P]ATP, 30 ng of cvRTP, and MgCl₂, MnCl₂, or CoCl₂ as indicated were incubated for 15 min at 37°C. ³²P_i release is plotted as a function of divalent cation concentration. (B) Reaction mixtures (10 μl) containing 50 mM Tris-HCl (pH 7.5), 0.2 mM [γ-³²P]ATP, 30 ng of cvRTP, 1 mM MnCl₂, and either MgCl₂, CaCl₂, CuSO₄, or ZnSO₄ at the concentration specified were incubated for 15 min at 37°C. The extents of ATP hydrolysis in the presence of manganese plus magnesium, calcium, copper, or zinc were normalized to the control activity in the presence of manganese alone (defined as 1.0).