Abstract
Thermodynamics of the enzyme-catalyzed (alkaline phosphatase, EC 3.1.3.1) hydrolysis of glucose 6-phosphate, mannose 6-phosphate, fructose 6-phosphate, ribose 5-phosphate, and ribulose 5-phosphate have been investigated using microcalorimetry and, for the hydrolysis of fructose 6-phosphate, chemical equilibrium measurements. Results of these measurements for the processes sugar phosphate2- (aqueous) + H2O (liquid) = sugar (aqueous) + HPO2++-(4) (aqueous) at 25 degrees C follow: delta Ho = 0.91 +/- 0.35 kJ.mol-1 and delta Cop = -48 +/- 18 J.mol-1.K-1 for glucose 6-phosphate; delta Ho = 1.40 +/- 0.31 kJ.mol-1 and delta Cop = -46 +/- 11 J.mol-1.dK-1 for mannose 6-phosphate; delta Go = -13.70 +/- 0.28 kJ.mol-1, delta Ho = -7.61 +/- 0.68 kJ.mol-1, and delta Cop = -28 +/- 42 J.mol-1.K-1 for fructose 6-phosphate; delta Ho = -5.69 +/- 0.52 kJ.mol-1 and delta Cop = -63 +/- 37 J.mol-1.K-1 for ribose 5-phosphate; and delta Ho = -12.43 +/- 0.45 kJ.mol-1 and delta Cop = -84 +/- 30 J.mol-1.K-1 for the hydrolysis of ribulose 5-phosphate. The standard state is the hypothetical ideal solution of unit molality. Estimates are made for the equilibrium constants for the hydrolysis of ribose and ribulose 5-phosphates. The effects of pH, magnesium ion concentration, and ionic strength on the thermodynamics of these reactions are considered.
Highlights
From the Laboratory of Metabolism and Molecular Biology,National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Rockvilk, Maryland 20852
Thethermodynamicsoftheenzyme-catalyzed hydrolysis of glucose calorimetric and equilibrium studies
Concentrations of fructose 6-phOSphate were determined using an enzymatic method of analysis [23], whereas concentrations of fructose were determined using high pressure liquid chromatography (HPLC).' The latteranalysis used a Bioequilibrium measurements
Summary
From the Chemical Thermodynamics Division, National Bureau of Standards, Gaithersburg,Maryland 20899. Concentrations of fructose 6-phOSphate were determined using an enzymatic method of analysis [23], whereas concentrations of fructose were determined using high pressure liquid chromatography (HPLC).' The latteranalysis used a Bioequilibrium measurements. Results of these measure- Rad Aminex HPX-87C column and conditions which have been. Attempts were made to use HPLC for determination of the concentrations of the sugar phosphates. J*mol"*K" for ribose 5-phosphate; aAnHdo = -12.43 of the method, and we do not have confidence in the concentrations f 0.45 kJ-mol" and ACE = -84 C 30 J-mol"*K" for obtained using the existing techniques.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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
