Tewari Y B, Goldberg R N
Chemical Thermodynamics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
J Biol Chem. 1989 Mar 5;264(7):3966-71.
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 beta-glucosidase, isomaltase, and maltase. The thermodynamic parameters obtained for the hydrolysis reactions, disaccharide(aq) + H2O(liq) = 2 glucose(aq), at 298.15 K are: K greater than or equal to 155, delta G0 less than or equal to -12.5 kJ mol-1, and delta H0 = -2.43 +/- 0.31 kJ mol-1 for cellobiose; K = 17.9 +/- 0.7, delta G0 = -7.15 +/- 0.10 kJ mol-1 and delta H0 = 2.26 +/- 0.48 kJ mol-1 for gentiobiose; K = 17.25 +/- 0.7, delta G0 = -7.06 +/- 0.10 kJ mol-1, and delta H0 = 5.86 +/- 0.54 kJ mol-1 for isomaltose; and K greater than or equal to 513, delta G0 less than or equal to -15.5 kJ mol-1, and delta H0 = -4.02 +/- 0.15 kJ mol-1 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-1 K-1; the heat capacity changes are approximately equal to zero J mol-1 K-1. Additional pathways for calculating thermodynamic parameters for these hydrolysis reactions are discussed.
利用高压液相色谱法和微量量热法研究了纤维二糖、龙胆二糖、异麦芽糖和麦芽糖的酶促水解热力学。水解反应在pH值为5.65的乙酸钠水溶液缓冲液中进行，温度范围为286至316K，使用的酶有β-葡萄糖苷酶、异麦芽糖酶和麦芽糖酶。在298.15K下，水解反应二糖（水溶液）+H₂O（液体）=2葡萄糖（水溶液）得到的热力学参数为：纤维二糖的K≥155，ΔG⁰≤-12.5kJ/mol，ΔH⁰=-2.43±0.31kJ/mol；龙胆二糖的K = 17.9±0.7，ΔG⁰=-7.15±0.10kJ/mol，ΔH⁰=2.26±0.48kJ/mol；异麦芽糖的K = 17.25±0.7，ΔG⁰=-7.06±0.10kJ/mol，ΔH⁰=5.86±0.54kJ/mol；麦芽糖的K≥513，ΔG⁰≤-15.5kJ/mol，ΔH⁰=-4.02±0.15kJ/mol。标准态是假设的单位质量摩尔浓度的理想溶液。由于葡萄糖对酶的抑制作用，无法获得纤维二糖或麦芽糖水解平衡常数的可靠值。水解反应的熵变范围为32至43J/mol·K；热容变化约等于零J/mol·K。讨论了计算这些水解反应热力学参数的其他途径。
