Effect of manganese(ous) and sulfate on activity of human placental glucose 6-phosphate-dependent form of glycogen synthase.
The human placental glucose-6-P-dependent form of glycogen synthase, in the absence of glucose-6-P, can be activated by MnSO4. Separately, Mn2+ and SO4(2-) have no significant effect. In the presence of glucose-6-P, Mn2+ activates the enzyme, but SO4(2-) inhibits; MnSO4 synergetically increases the enzyme activity. Mn2+ reduces the Ka for glucose-6-P to one-tenth of the control value; SO4(2-) increases the Ka 5-fold; however, MnSO4 has no effect on Ka. MnSO4, like glucose-6-P, increases the Vmax of the enzyme in the presence of its substrate, UDP-glucose; it slightly increases the Km for UDP-glucose. In the presence of glucose-6-P, Mn2+ increases and SO4(2-) decreases the Vmax of the enzyme, but neither has an effect on the Km for UDP-glucose. At physiological concentrations of UDP-glucose and glucose-6-P, either Mn2+ or MnSO4 at concentrations less than 1 mM increases the enzyme activity as much as 8 mM glucose-6-P does. At physiological concentrations of UDP-glucose and glucose-6-P, Mn2+ or MnSO4 reverses the inhibition of the enzyme by ATP.
D002712:Chlorides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005958:Glucosephosphates / Q000494:pharmacology; D006006:Glycogen Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology*; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D013431:Sulfates / Q000494:pharmacology*; D013890:Thiourea / Q000494:pharmacology; D014532:Uridine Diphosphate Glucose / Q000378:metabolism
D002712:Chlorides; D005958:Glucosephosphates; D013431:Sulfates; D008345:Manganese; D006006:Glycogen Synthase; D013890:Thiourea; D008274:Magnesium; D014532:Uridine Diphosphate Glucose