Reversible effect of calcium-binding protein regucalcin on the Ca2+-induced inhibition of deoxyuridine 5′-triphosphatase activity in rat liver cytosol

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on deoxyuridine 5′-triphosphatase (dUTPase) in the cytosol of rat liver was investigated. Addition of Ca²⁺ up to 5.0 μM to the enzyme reaction mixture caused a significant decrease of dUTPase activity, while Zn²⁺, Cd²⁺, Co²⁺, Al³⁺, Mn²⁺ and Ni²⁺ (10 μM) did not have an appreciable effect. The Ca²⁺-induced decrease of dUTPase activity was reversed by the presence of regucalcin; the effect was complete at 1.0 μM of the protein. Regucalcin had no effect on the basal activity of the enzyme. Meanwhile, the reversible effect of regucalcin on the Ca²⁺ (10 μM)-induced decrease of dUTPase activity was not altered by the coexistence of Cd²⁺ or Zn²⁺ (10 μM). The present data suggest that liver cytosolic dUTPase is uniquely regulated by Ca²⁺ of various metals, and that the Ca²⁺ effect is reversed by regucalcin.