Goldberg R N, Tewari Y B
Chemical Thermodynamics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
J Biol Chem. 1989 Jun 15;264(17):9897-900.
The thermodynamics of the hydrolysis of lactose to glucose and galactose have been investigated using both high pressure liquid chromatography and heat-conduction microcalorimetry. The reaction was carried out over the temperature range 282-316 K and in 0.1 M sodium acetate buffer at a pH of 5.65 using the enzyme beta-galactosidase to catalyze the reaction. For the process lactose(aq) + H2O(liq) = glucose(aq) + galactose(aq), delta G0 = -8.72 +/- 0.20 kJ.mol-1, K0 = 34 +/- 3, delta H0 = 0.44 +/- 0.11 kJ.mol-1, delta S0 = 30.7 +/- 0.8 J.mol-1.K-1, and delta Cop = 9 +/- 20 J.mol-1.K-1 at 298.15 K. The standard state is the hypothetical ideal solution of unit molality. Thermochemical cycle calculations using enthalpies of combustion and solution, entropies, solubilities, activity coefficients, and apparent molar heat capacities have also been performed. These calculations indicate large discrepancies which are attributable primarily to errors in literature data on the enthalpies of combustion and/or third law entropies of the crystalline forms of the substrates.
利用高压液相色谱法和热导微量量热法研究了乳糖水解为葡萄糖和半乳糖的热力学。该反应在282 - 316 K的温度范围内进行，在pH值为5.65的0.1 M醋酸钠缓冲液中，使用β - 半乳糖苷酶催化反应。对于乳糖（水溶液）+ H₂O（液体）=葡萄糖（水溶液）+半乳糖（水溶液）这一过程，在298.15 K时，ΔG⁰ = -8.72 ± 0.20 kJ·mol⁻¹，K⁰ = 34 ± 3，ΔH⁰ = 0.44 ± 0.11 kJ·mol⁻¹，ΔS⁰ = 30.7 ± 0.8 J·mol⁻¹·K⁻¹，以及ΔCₚ = 9 ± 20 J·mol⁻¹·K⁻¹。标准态是假设的单位质量摩尔浓度的理想溶液。还进行了利用燃烧热和溶解热、熵、溶解度、活度系数以及表观摩尔热容的热化学循环计算。这些计算表明存在较大差异，这主要归因于关于底物晶体形式的燃烧热和/或第三定律熵的文献数据中的误差。
