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-mu-M to the enzyme reaction mixture caused a significant decrease of dUTPase activity, while Zn2+, Cd2+, Co2+, Al3+, Mn2+ and Ni2+ (10-mu-M) 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-mu-M of the protein. Regucalcin had no effect on the basal activity of the enzyme. Meanwhile, the reversible effect of regucalcin on the Ca2+ (10-mu-M)-induced decrease of dUTPase activity was not altered by the coexistence of Cd2+ or Zn2+ (10-mu-M). 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.