Figure 4.

Ca²⁺ uptake in the presence of other divalent cations. The ⁴⁵Ca²⁺ uptake by the pea Golgi vesicles was measured at 25°C for 1.5 min, in an incubation buffer containing 870 nm free Ca²⁺ (4 times pump K_m), 2 mm ATP, and 3 mm MgCl₂. Experiments were carried out in the absence and in the presence of increasing concentrations (870 nm, 1.47 μm, 4.35 μm, and 8.70 μm) of each of the following divalent cations: Cu²⁺, Co²⁺, Mn²⁺, Fe²⁺, and Cd²⁺. Values of the Ca²⁺ uptake at 1.5 min in the presence of different concentrations of the divalent cations are expressed as a percentage of the Ca²⁺ uptake measured in the absence of other cations (6.3 ± 0.2 nmol mg⁻¹).