Effects of Ca2+ and V5+ on Glucose-6-phosphatase Activity in Rat Liver Microsomes: The Ca2+ Effect Is Reversed by Regucalcin

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 um to the enzyme reaction mixture caused a significant increase of glucose-6-phosphatase activity in hepatic microsomes, while Ni2*, Zn2+, Cd2*, Cu2+, Mn22 and Co22 (20/lm) did not have an appreciable effect. Vanadate (V5+) markedly inhibited the enzyme activity; a significant inhibitory effect was seen at 10 UM Vs+. The Ca2+-induced increase of glucose-6-phosphatase activity was reversed by the presence of regucalcin; the effect was complete at 1.0 UM of the protein. Regucalcium had no effect on the basal activity of the enzyme. Meanwhile, the inhibitory effect of V5+ (10—100 uM) on glucose-6-phosphatase was not appreciably blocked by the presence of regucalcin (up to 2.0/im). 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+. © 1989, The Pharmaceutical Society of Japan. All rights reserved.