Andrade M I, Jones M N, Skinner H A
Eur J Biochem. 1976 Jun 15;66(1):127-31. doi: 10.1111/j.1432-1033.1976.tb10432.x.
The enthalpies of interaction of urea with five globular proteins, ribonuclease A, trypsin, beta-lacto-globulin, ovalbumin and bovine serum albumin have been measured in aqueous solution at pH 7.0, I=0.005 M and 25 degrees C over a range of urea molality m from 0-15 mmol g-1 (where a 1 molal solution contains 1 mmol g-1). For all the proteins the interaction is exothermic, and there is an appreciable heat evolution at low urea concentrations, m less than 5 mmol g-1, which increases sharply at higher urea concentrations when the proteins undergo unfolding. If account is taken of the endothermic enthalpies of unfolding of the native proteins, the enthalpies of interactions of urea per unit mass denatured protein lie in the range -45 to -75 J g-1, corresponding to an average binding enthalpy of -23 kJ mol-1 bound urea.
在pH 7.0、离子强度I = 0.005 M、25℃的水溶液中，测定了尿素与五种球状蛋白质（核糖核酸酶A、胰蛋白酶、β-乳球蛋白、卵清蛋白和牛血清白蛋白）在尿素质量摩尔浓度m为0 - 15 mmol g⁻¹范围内（其中1质量摩尔溶液含有1 mmol g⁻¹）的相互作用焓。对于所有蛋白质，这种相互作用都是放热的，并且在低尿素浓度（m < 5 mmol g⁻¹）时有明显的热释放，当蛋白质发生去折叠时，在较高尿素浓度下热释放急剧增加。如果考虑天然蛋白质去折叠的吸热焓，每单位质量变性蛋白质的尿素相互作用焓在-45至-75 J g⁻¹范围内，对应于结合尿素的平均结合焓为-23 kJ mol⁻¹。
