Effect of calcium-binding protein on adenosine 5'-triphosphatase activity in the brain cytosol of rats of different ages: the inhibitory role of regucalcin.

Adenosine 5'-triphosphatase (ATPase) plays a role in the process of energy conversion in the controlled hydrolysis of ATP. The effect of Ca2+ -binding protein on ATPase activity in the brain cytosol of rats of different ages was investigated. ATPase activity in the brain cytosol of 50-week-old rats was significantly decreased as compared with that of 5-week-old rats. The presence of calcium chloride (10(-5) and 10(-4) M) in the enzyme reaction mixture caused a significant increase in ATPase activity in the brain cytosol of rats of different ages. This increase was not altered by trifluoperazine (2x10(-5) M), an antagonist of calmodulin. Calmodulin (5 microg/ml), calbindin (5 microg/ml) or S-100A protein (10 microg/ml), a Ca2+ -binding protein, had no effect on ATPase activity. Meanwhile, regucalcin (10(-9) M), which is present in brain, significantly decreased ATPase activity in young and older rats. However, the effect of regucalcin was weakened by the presence of Ca2+ (10(-5) M). The addition of anti-regucalcin monoclonal antibody in the reaction mixture caused a significant elevation of ATPase activity; this increase was completely abolished by addition of regucalcin (10(-9) M). The present study suggests that regucalcin plays an inhibitory role in the regulation of ATPase activity in the brain cytosol of rats of different ages.