Abstract
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.
Highlights
From the Section on Developmental Enzymology, Laboratory ofBiomedical of Child Health and Human Development, National Institutes of Health, Sciences, National Bethesda, Maryland
In the presence of glucose-6-P, Mn’+ increases and SO,‘- decreases the V, of the enzyme, but neither has an effect on the K, for UDP-glucose
In the presence of glucose-6-P, the enzyme activity is increased by the addition of MnSO, (Fig. lA)
Summary
From the Section on Developmental Enzymology, Laboratory ofBiomedical of Child Health and Human Development, National Institutes of Health, Sciences, National Bethesda, Maryland. The human placental glucose-6-P-dependent form of glycogen synthase, in the absence of glucose-&P, can be activated by MnSO,. MnSO,, like glucose-&P, increases the Y,;,, of the enzyme in the presence of its substrate, the K,,, for UDP-glucose.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
