Jacobson A L, Turner C L
Biochemistry. 1980 Sep 16;19(19):4534-8. doi: 10.1021/bi00560a023.
Differential scanning calorimetry has been used to study the thermal denaturation of ribonuclease in aqueous dimethyl sulfoxide and acqueous p-dioxane. A two-state reversible denaturation occurs in acqueous dimethyl sulfoxide. The denaturation is irreversible in aqueous p-dioxane. The transition temperatuire decreases in both organic solvents, with p-dioxane producing a considerably greater effect. The enthalpy of the denaturation initially increases with increasing dimethyl sulfoxide concentration and then decreases at high concentrations. Similar behavior is observed in the entropy in the dimethyl sulfoxide solutions. The enthalpy of the denaturation decreases markedly with low p-dioxane concentrations. Changes in pH due to presence of organic solvent cannot account for the changes in enthalpy of denaturation. Addition of organic solvent tends to increase the pH of the ribonuclease solution. Higher pH in aqueous solutions gives a high transition temperature, whereas addition of organic solvent results in the opposite bahavior. The relative changes in the two solvents systems suggest that specific solvent effects occur and that destablization of the native state relative to the denatured state is greater with p-dioxane than with dimethyl sulfoxide.
差示扫描量热法已被用于研究核糖核酸酶在二甲基亚砜水溶液和对二氧六环水溶液中的热变性。在二甲基亚砜水溶液中发生两态可逆变性。在对二氧六环水溶液中变性是不可逆的。两种有机溶剂中的转变温度均降低，对二氧六环的影响更为显著。变性焓最初随二甲基亚砜浓度的增加而增加，然后在高浓度时降低。在二甲基亚砜溶液中熵也观察到类似行为。在低对二氧六环浓度下，变性焓显著降低。由于有机溶剂的存在导致的pH变化不能解释变性焓的变化。添加有机溶剂往往会使核糖核酸酶溶液的pH升高。水溶液中较高的pH值会导致较高的转变温度，而添加有机溶剂则会产生相反的行为。两种溶剂体系中的相对变化表明存在特定的溶剂效应，并且相对于变性态，天然态的去稳定化在对二氧六环中比在二甲基亚砜中更大。
