title: Enhanced glucose 6-phosphatase activity in liver of rats exposed to Mg(2+)-deficient diet.
abstract: Total hepatic Mg(2+) content decreases by >25% in animals maintained for 2 weeks on Mg(2+) deficient diet, and results in a >25% increase in glucose 6-phosphatase (G6Pase) activity in isolated liver microsomes in the absence of significant changed in enzyme expression. Incubation of Mg(2+)-deficient microsomes in the presence of 1mM external Mg(2+) returned G6Pase activity to levels measured in microsomes from animals on normal Mg(2+) diet. EDTA addition dynamically reversed the Mg(2+) effect. The effect of Mg(2+) or EDTA persisted in taurocholic acid permeabilized microsomes. An increase in G6Pase activity was also observed in liver microsomes from rats starved overnight, which presented a ~15% decrease in hepatic Mg(2+) content. In this model, G6Pase activity increased to a lesser extent than in Mg(2+)-deficient microsomes, but it could still be dynamically modulated by addition of Mg(2+) or EDTA. Our results indicate that (1) hepatic Mg(2+) content rapidly decreases following starvation or exposure to deficient diet, and (2) the loss of Mg(2+) stimulates G6P transport and hydrolysis as a possible compensatory mechanism to enhance intrahepatic glucose availability. The Mg(2+) effect appears to take place at the level of the substrate binding site of the G6Pase enzymatic complex or the surrounding phospholipid environment.
authors.affiliation: Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106-4970, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Barfell
authors.forename: Ashlee
authors.initials: A
authors.lastname: Crumbly
authors.forename: Andrea
authors.initials: A
authors.lastname: Romani
mesh_terms: D000818:Animals; D001692:Biological Transport; D004032:Diet; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013217:Starvation / Q000201:enzymology / Q000378:metabolism
chemical_list: D005952:Glucose-6-Phosphatase; D008274:Magnesium