Effects of Ca2+ and V5+ on glucose-6-phosphatase activity in rat liver microsomes. The Ca2+ effect is reversed by regucalcin.

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Abstract
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 Ca2+ up to 2.5 .mu.M to the enzyme reaction mixture caused a significant increase of glucose-6-phosphatase activity in hepatic microsomes, while Ni2+, Zn2+, Cd2+, Cu2+, Mn2+ and Co2+ (20 .mu.M) did not have an appreciable effect. Vanadate (V5+) markedly inhibited the enzyme activity; a significant inhibitory effect was seen at 10 .mu.M V5+. The Ca2+-induced increase of glucose-6-phosphatase activity was reversed by the presence of regucalcin; the effect was complete at 1.0 .mu.M of the protein. Regucalcium had no effect on the basal activity of the enzyme. Meanwhile, the inhibitory effect of V5+ (10.sbd.100 .mu.M) on glucose-6-phosphatase was not appreciably blocked by the presence of regucalcin (up to 2.0 .mu.M). The present data suggest that hepatic microsomal glucose-6-phosphatase is uniquely regulated by Ca2+ and V5+, of various metals, and that the Ca2+ 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 Ca2+.

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