Observation of uridine triphosphate:glucose-1-phosphate uridylyltransferase activity in maize root tips by saturation transfer 31P-NMR. Estimation of cytoplasmic PP.
Saturation transfer 31P nuclear magnetic resonance was used to estimate the unidirectional rate of phosphorus exchange between Glc-1-P and UDPGlc in maize root tips. The rate was determined to be approx. 4 mumol.min-1 per g fresh weight. This estimated rate is much higher than net rates of other reactions in glucose metabolism (e.g., more than 10-times faster than the maximal glycolytic flux in this tissue). Furthermore, exchange between Glc-1-P and UDPGlc was not significantly inhibited by the metabolic poison KCN. We conclude that the unidirectional rate of conversion of Glc-1P to UDPGlc is much faster than the net rate of UDPGlc synthesis--the UTP:Glc-1-P uridylyltransferase reaction is near-equilibrium in vivo. From the equilibrium constant for this transferase reaction and the concentrations of Glc-1-P, UTP and UDPGlc, the level of cytoplasmic PPi was estimated to be approx. 10 nmol.g-1.
Roberts
J K
JK
Department of Biochemistry, University of California, Riverside 92521.
D003593:Cytoplasm / Q000378:metabolism; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000378:metabolism*; D003313:Zea mays / Q000201:enzymology*
D010758:Phosphorus; D009713:Nucleotidyltransferases; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase; D014544:Uridine Triphosphate