热变性前后水合醛缩酶中水状态的热力学研究

 用差示扫描量热计,测定了不同水合态(水含量h从0.08g/g至2.50g /g)冻结的水合醛缩酶样品中冰的熔化温度和熔化焓,并计算出熔化熵。实验结果表明,变性前,水合醛缩酶中的水转化成四种状状:(1)不冻结水,(2)熔化焓和熔化温度均低了普通水的可冻结水,(3)熔化焓与普通水相同而熔化温度低于普通水的可冻结水,(4)熔化焓和熔化温度均与普通水相同的容积水。变性后,水合醛缩酶中的水可处于五种状态,即不冻结水,熔化焓低于普通水而熔化温度与普通水相同的可冻结水,以及熔化温度均低于普通水且彼此不相同的三种状态的可冻结水。实验还观察到,水合醛缩酶在热变性前后,水在这些态中的量是不同的。

STUDY OF THERMODYNAMICS OF WATER STATE IN HYDRATED ALDOLASE BEFORE AND AFTER DENATURATION

The temperature and enthalpy of melting of ice in the frozen hydrated aldolase (water content in the range from 0.08 to 2.50g of water per g of protein) were measured with differential scanning calorimeter in the temperature range from -40℃ to 20℃. The entropy of melting of ice was caculated also. The experimental resulte showed that the absorbed water in the hydrated aldolase could be resolved into four states before denaturation. The four states are. (1)water not freezable on cooling to -40℃, (2)freezable water with both entropy and temperature of melting below the values for ordinary water, (3)freezable water with the enthalpy of melting of ordinary water and the temperature of melting below the value for ordinary water, (4)freezable water not distinguished from ordinary water. The absorbed water could be resolved into five states after hydrated aldolase denaturation. The five states are the water not freezable, the freezable water with the temperature of melting of ordinary water and the enthalpy of melting below the value for ordinary water, and three freezable waters with different temperatures of melting below the value for ordinary water.