Stimulatory effect of calcium-binding protein regucalcin on phosphatase activity in the brain cytosol of rats with different ages.

The effect of calcium-binding protein regucalcin on phosphatase activity in the brain cytosol of rats with different ages was investigated. The presence of regucalcin (10(-8) and 10(-7) M) in the enzyme reaction mixture caused a significant increase of neutral p-nitrophenylphosphatase activity in the brain cytosol obtained from 5- and 50-week-old rats. This increase was seen in the absence or presence of calmodulin (2 microg/mL) and calcium chloride (100 microM). Brain cytosolic phosphatase activity was not significantly altered by S-100A (10(-6) M) or calbindin (10(-7) M), which is a calcium-binding protein. Regucalcin-increased phosphatase activity was clearly decreased by N-ethylmaleimide, a modifying reagent of thiol(SH)-group, suggesting that regucalcin acts on the SH-group of the enzyme. Moreover, the presence of anti-regucalcin monoclonal antibody (50-200 ng/mL) in the reaction mixture caused a significant decrease of brain cytosolic phosphatase activity, suggesting that the endogenous regucalcin has a stimulatory effect on the enzyme activity. These results suggest that regucalcin plays a role in the regulation of protein phosphatase in rat brain cytosol.