Activation of Hepatic Microsomal Ca^<2+>-Adenosine Triphosphatase by Calcium-Binding Protein Regucalcin

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The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on Ca^<2+>-adenosine triphosphatase (ATPase) activity in hepatic microsomes was investigated. Mg^<2+>-ATPase activity was clearly increased by the presence of 50 μM Ca^<2+>. Regucalcin (1.0-4.0 μM) caused a remarkable elevation (about 3-fold) of Ca^<2+>-ATPase activity. Also, Mg^<2+>-ATPase activity was increased (about 1.6-fold) by the presence of regucalcin (2.0 and 4.0 μM). Guanosine-5'-O-(3-thiotriphosphate) (GTP_rs; 10^<-5> and 10^<-4> M) and nicotinamide adenine dinucleotide phosphate oxidized form (NADP^+; 10^<-5> to 10^<-3> M) or reduced form (NADPH; 10^<-4> and 10^<-3> M) significantly increased Ca^<2+>-ATPase activity. These increases were not enhanced by the presence of regucalcin (2.0 μM). Of various metal ions, a comparatively low concentration of V^<5+> (10^<-5> M) or Cd^<2+> (10^<-6> M) significantly increased Ca^<2+>-ATPase activity, while Hg^<2+>, Zn^<2+>, Cu^<2+> and Mn^<2+> did not have such an effect. Regucalcin (2.0 μM) did not enhance the effect of V^<5+> and Cd^<2+> on Ca^<2+>-ATPase activity. The present finding, that regucalcin activates hepatic microsomal Ca^<2+>-ATPase, suggests a cell physiological role of regucalcin as an activator in the microsomal Ca^<2+>-pump activity. This action of regucalcin may not be influenced by other regulators.
公益社団法人日本薬学会の論文
1989-04-25