Effects of Ca^<2+> and V^<5+> on Glucose-6-phosphatase Activity in Rat Liver Microsomes : The Ca^<2+> Effect Is Reversed by Regucalcin

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The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on glucose-6-phosphatase in the microsomes of rat liver was investigated. Addition of Ca^<2+> up to 2.5 μM to the enzyme reaction mixture caused a significant increase of glucose-6-phosphatase activity in hepatic microsomes, while Ni^<2+>, Zn^<2+>, Cd^<2+>, Cu^<2+>, Mn^<2+> and Co^<2+> (20 μM) did not have an appreciable effect. Vanadate (V^<5+>) markedly inhibited the enzyme activity; a significant inhibitory effect was seen at 10 μM V^<5+>. The Ca^<2+>-induced increase of glucose-6-phosphatase activity was reversed by the presence of regucalsin; the effect was complete at 1.0 μM of the protein. Regucalcium had no effect on the basal activity of the enzyme. Meanwhile, the inhibitory effect of V^<5+> (10-100 μM) on glucose-6-phosphatase was not appreciably blocked by the presence of regucalcin (up to 2.0 μM). The present data suggest that hepatic microsomal glucose-6-phosphatase is uniquely regulated by Ca^<2+> and V^<5+>, of various metals, and that the Ca^<2+> effect is reversed by regucalcin. The present study supports the view that regucalcin plays an important role as a regulatory protein in liver cell function related to Ca^<2+>.
公益社団法人日本薬学会の論文
1989-02-25