THERMODYNAMICS OF HYDROLYSIS OF OLIGOSACCHARIDES

Microcalorimetry has been used to determine enthalpy changes for the hydrolysis of a series of oligosaccharides. High-pressure liquid chromatography was used to determine the extents of reaction and to check for any possible side reactions. The enzyme glucan 1,4-alpha-glucosidase was used to bring about the following hydrolysis reactions: (A) maltose(aq) + H2O(liq) = 2D-glucose(aq); (B) maltotriose(aq) + 2H2O(liq) = 3D-glucose(aq); (C) maltotetraose(aq) + 3H2O(liq) - 4D-glucose(aq); (D) maltopentaose(aq) + 4H2O(liq) = 5D-glucose(aq); (E) maltohexaose(aq) + 5H2O(liq) = 6D-glucose(aq); (F) maltoheptaose(aq) + 6H2O(liq) = 7D-glucose(aq); (G) amylose(aq) + nH2O(liq) = (n + 1) D-glucose(aq); and (H) panose(aq) + 2H2O(liq) = 3D-glucose(aq); (J) isomaltotriose(aq) + 2H2O(liq) = 3D-glucose(aq). The enzyme beta-fructofuranosidase was used for the reactions: (K) raffinose(aq) + H2O(liq) = alpha-D-melibiose(aq) + D-fructose(aq); and (L) stachyose(aq) + H2O(liq) = o-alpha-D-galactopyranosyl-(1 --> 6)-alpha-o-D-galactopyranosyl-(1 --> 6)-alpha-D-glucopyranose + D-fructose(aq). The results of the calorimetric measurements (298.15 K, 0.1 M sodium acetate buffer, pH 4.44-6.00) are: DELTA-H(A)degrees = -4.55 +/- 0.10, DELTA-H(B)degrees = -9.03 +/- 0.10, DELTA-H(C)degrees = -13.79 +/- 0.15, DELTA-H(D)degrees = -18.12 +/- 0.10, DELTA-H(E)degrees = -22.40 +/- 0.15, DELTA-H(F)degrees = -26.81 +/- 0.20, DELTA-H(H)degrees = 1.46 +/- 0.40, DELTA-H(J)degrees = 11.4 +/- 2.0, DELTA-H(K)degrees = -15.25 +/- 0.20, and DELTA-H(L)degrees = -14.93 +/- 0.20 kJ mol-1. The enthalpies of hydrolysis of two different samples of amylose were 1062 +/- 20 and 2719 +/- 100 kJ mol-1, respectively. These processes correspond to the hydrolysis of the following linkages: glucose-glucose (alpha,1 --> 4) glucose-glucose (alpha,1 --> 6), and glucose-fructose (1 --> 6). The respective enthalpy changes accompanying the hydrolysis of these linkages are -4.53, 5.8 and -15.0 kJ mol-1. Both these results and available thermodynamic data in the literature demonstrate that additivity works well in predicting the thermodynamics of hydrolysis reactions involving oligosaccharides.