title: Thermodynamics of hydrolysis of sugar phosphates.
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.
authors.affiliation: Chemical Thermodynamics Division, National Bureau of Standards, Gaithersburg, Maryland 20899.
authors.forename: Y B
authors.initials: YB
authors.lastname: Tewari
authors.forename: D K
authors.initials: DK
authors.lastname: Steckler
authors.forename: R N
authors.initials: RN
authors.lastname: Goldberg
authors.forename: W L
authors.initials: WL
authors.lastname: Gitomer
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D002151:Calorimetry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D013403:Sugar Phosphates; D013816:Thermodynamics
chemical_list: D013403:Sugar Phosphates; D000469:Alkaline Phosphatase