Regucalcin increases superoxide dismutase activity in rat liver cytosol

The effect of regucalcin, a regulatory protein in the intracellular signaling process, on superoxide dismutase (SOD) activity in the cytosol of rat liver was investigated. The presence of zinc sulfate (10(-6) or 10(-5) m) or cupric sulfate (10(-6) m) in the enzyme reaction mixture caused a significant increase in SOD activity, indicating that Cu/Zn-SOD may be present in the liver cytosol. SOD activity was significantly increased by the addition of regucalcin (0.1, 0.25, or 0.5 microM) to the reaction mixture. The presence of dithiothreitol (DTT; 0.1, 0.5, or 1.0 mM), a protective reagent for the sulfhydryl group, caused a significant decrease in SOD activity. The effect of regucalcin (0.25 microM) in increasing SOD activity was not seen in the presence of DTT (1.0 mM). Meanwhile, SOD activity was significantly raised by the addition of N-ethylmaleimide (NEM; 0.5 or 1.0 mM), a modifying reagent for the sulfhydryl reagent. Regucalcin (0.25 microM) caused a significant increase in SOD activity in the presence of NEM (1.0 mM). The effect of regucalcin in increasing SOD activity may not involve the sulfhydryl group of SOD. This study demonstrates that regucalcin has an activatory effect on SOD in the liver cytosol of rats.