Calcium-Binding Protein Regucalcin Is an Activator of (Ca^<2+>-Mg^<2+>)-Adenosine Triphosphatase in the Plasma Membranes of Rat Liver

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The effect of regucalcin, a calcium-binding protein isolaetd from rat liver cytosol, on (Ca^<2+>-Mg^<2+>)-adenosine triphosphatase (ATPase) activity in the plasma membranes of rat liver was investigated. ^<125>I-Regucalcin bound to the plasma membranes in the presence or absence of 0.1 mM Ca^<2+>. Regucalcin (0.35 μM) increased the plasma membrane (Ca^<2+>-Mg^<2+>)-ATPase activity about 15% (p<0.01), and a higher concentration (4.0 μM) showed a remarkable effect. Also, regucalcin (0.35-2.0 μM) markedly increased the plasma membrane Mg^<2+>-ATPase activity in the absence of Ca^<2+>. The effect of regucalcin on (Ca^<2+>-Mg^<2+>)-ATPase activity was not regulated by the presence of guanosine-5'-O-(3-thiotriphosphate) (10^<-5> and 10<-4>M), glucagon (10^<-6> and 10^<-5>M) or norepinephrine (10^<-7>-10<-5>M), suggesting that the regucalcin effect is not linked to guanosine triphosphate (GTP)-binding protein in the plasma membranes. Vanadium (10 and 10 μM), which inhibits the phosphorylation of liver plasma membrane (Ca^<2+>-Mg^<2+>)-ATPase, decreased the enzyme activity about 20% (p<0.01). This decrease was completely restored by the presence of regucalcin (1.0 μM). The present results indicate that regucalcin binds to the plasma membranes of liver cells and increases the (Ca^<2+>-Mg^<2+>)-ATPase activity. Regucalcin may be an activator of (Ca^<2+>-Mg^<2+>)-ATPase in the plasma membranes.
公益社団法人日本薬学会の論文
1988-09-25