Suppressive effect of endogenous regucalcin on guanosine triphosphatase activity in rat liver nucleus.

Abstract

The effect of regucalcin, a regulatory protein of Ca2+ signaling, on guanosine triphosphatase (GTPase) activity in the nuclei of rat liver was investigated. GTPase activity was significantly increased by the addition of CaCl2 (50 microm) in the enzyme reaction mixture. This increase was not seen in the presence of trifluoperazine (25 microM), an antagonist of calmodulin, which could decrease nuclear GTPase activity, suggesting that nuclear endogenous calmodulin is involved in an increase in the enzyme activity related to Ca2+ addition. The presence of regucalcin (0.5 microM) in the enzyme reaction mixture caused a significant decrease in nuclear GTPase activity. The enzyme activity was significantly raised in the presence of anti-regucalcin monoclonal antibody (25 and 50 ng/ml) in the reaction mixture. This increase was completely abolished by the addition of regucalcin (0.5 microM). Also, the effect of regucalcin addition in increasing nuclear GTPase activity was seen in the presence of EGTA (0.1 mM), a chelator of Ca2+. The present study demonstrates that endogenous regucalcin has a suppressive effect on GTPase activity in the nuclei of rat liver.