Effect of anti-regucalcin antibody on neutral phosphatase activity in rat liver cytosol: involvement of endogenous regucalcin.

The effect of anti-regucalcin monoclonal antibody on neutral phoshatase activity in rat liver cytosol was investigated. Phosphotyrosine, phosphoserine, and phosphothreonine were used as the substrate toward phosphatase assay. Liver cytosolic phosphatase activity with three phosphoaminoacids was significantly increased in the presence of anti-regucalcin antibody (100 and 200 ng/ml) in the enzyme reaction mixture with calcium chloride (0.1 mM) or EGTA (1.0 mM). The effect of anti-regucalcin antibody was completely abolished in the presence of exogenous regucalcin (1.0 microM), indicating the involvement of endogenous regucalcin. The anti-regucalcin anti body- increased phosphatase activity was not significantly altered in the presence of trifluoperazine (20 microM), an antagonist of calmodulin, or akadaic acid ( 10 microM), an inhibitor of protein phosphatase, although these inhibitors caused a slight decrease in liver cytosolic phosphatase activity. The effect of endogenous regucalcin might be not related to calmodulin, and it was insensitive to okadaic acid. The present findings suggest that endogenous regucalcin is involved in the regulation of protein phasphatase in rat liver cytoplasm.