Some regulatory properties of a glucose-6-phosphate-dependent form of glycogen synthase purified from rabbit renal medulla.
Glycogen synthase D was purified greater than 1000-fold from rabbit renal medulla. The enzyme was almost completely dependent upon glucose-6-P for activity (activity ratio approximately equal to 0.01). The A0.5 for glucose-6-P activation was 420 microM when UDPGlc was present at 4.4 mM and the A0.5 was 2.23 mM when UDPGlc was present at physiological concentration (100 microM). The S0.5 for UDPGlc of glycogen synthase D was dependent on glucose-6-P. The S0.5 ranged from 250 to 70 microM when glucose-6-P was varied from 0.2 to 10 mM. The Vmax increased 3-fold. Inhibition of glycogen synthase D by ATP was competitive with respect to UDPGlc. The Ki for ATP inhibition was 340 microM. At physiological concentration of UDPGlc, the enzyme was inhibited 50% by 500 microM ATP. ATP inhibition was not reversed by glucose-6-P. These results suggest that renal medullary glycogen synthase D would be inactive at normal cellular concentrations of the substrate UDPGlc, the activator glucose-6-P, and the inhibitor ATP.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D004789:Enzyme Activation / Q000187:drug effects; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000494:pharmacology*; D006006:Glycogen Synthase / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D007679:Kidney Medulla / Q000201:enzymology*; D007700:Kinetics; D011817:Rabbits
D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; D000255:Adenosine Triphosphate; D006006:Glycogen Synthase