title: Regulation of UDPG pyrophosphorylase in Acetabularia mediterranea.
abstract: The kinetic properties of UDPG pyrophosphorylase (glucosyl-1-phosphate uridyl transferase, EC 2.7.7.9) suggest that it may play a key role in the regulation of metabolism in Acetabularia mediterranea. The enzyme-catalyzed reaction is readily reversible in vitro, and has been assayed in both directions. The enzyme shows substrate inhibition by UDPG and UTP at substrate concentrations in excess of 2 mM. The kinetic behavior of the enzyme is consistent with the hypothesis that it catalyzes an ordered bisubstrate biproduct reaction in which G-1-P is the leading substrate, and UTP is the leading product. A plot of initial velocity vs. PPi concentration is sigmoid, indicating a cooperative homotropic effect. PGAL inhibits the reaction in the direction: UTP + G-1-P leads to UDPG + PPi It has no effect on the reverse reaction. The responses of the enzyme may serve to regulate the allocation of G-1-P between anabolic and catabolic pathways.
mesh_terms: D000076:Acetabularia / Q000201:enzymology*; D000460:Chlorophyta / Q000201:enzymology*; D005958:Glucosephosphates; D007700:Kinetics; D009713:Nucleotidyltransferases / Q000378:metabolism*; D013379:Substrate Specificity; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014532:Uridine Diphosphate Glucose / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D005958:Glucosephosphates; C031590:glucose-1-phosphate; D009713:Nucleotidyltransferases; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase; D014544:Uridine Triphosphate; D014532:Uridine Diphosphate Glucose