Thermodynamics of Hydrolysis of Disaccharides

The thermodynamics of the enzymatic hydrolysis of cellobiose, gentiobiose, isomaltose, and maltose have been studied using both high pressure liquid chromatography and microcalorimetry. The hydrolysis reactions were carried out in aqueous sodium acetate buffer at a pH of 5.65 and over the temperature range of 286 to 316 K using the enzymes @-glucosidase, isomaltase, and maltase. The thermodynamic parameters obtained for the hydrolysis reactions, disaccharide(aq) + HzO(liq) = 2 glucose(aq), at 298.15 K are: K 2 155, AGO 5 -12.5 kJ mol-l, and AH" = -2.43 f 0.31 kJ mol" for cellobiose; K = 17.9 f 0.7, AGO = -7.15 f 0.10 kJ mol" and AH" = 2.26 f 0.48 kJ mol" for gentiobiose; K = 17.25 f 0.7, AGO = -7.06 f 0.10 kJ mol", and A H ' = 5.86 f 0.54 kJ mol" for isomaltose; and K a 513, AGO 5 -15.5 kJ mol", and A H ' = -4.02 f 0.15 kJ mol" for maltose. The standard state is the hypothetical ideal solution of unit molality. Due to enzymatic inhibition by glucose, it was not possible to obtain reliable values for the equilibrium constants for the hydrolysis of either cellobiose or maltose. The entropy changes for the hydrolysis reactions are in the range 32 to 43 J mol" K-I; the heat capacity changes are approximately equal to zero J mol" K-l. Additional pathways for calculating thermodynamic parameters for these hydrolysis reactions are discussed.