二氢叶酸还原酶天然状态可能存在两种构象

鸡肝二氢叶酸还原酶（ＤＨＦＲ）平衡态的去折叠曲线符合二态模型，但在４．０ｍｏｌ／Ｌ脲中的去折叠动力学为两相。该酶的ＡｒｒｅｈｉｕｓＰｌｏｔ有一个拐点，但在低浓度变性剂存在下，拐点消失。用二氢叶酸还原酶的天然状态存在两种构象可以很好地解释上述现象。二氢叶酸还原酶去折叠过程中没有稳定存在的中间体，动力学过程中的两相可能是两种天然构象态的去折叠速度常数不同造成的。ＡｒｒｅｈｉｕｓＰｌｏｔ的拐点是由于在不同的温度条件下，两种天然构象的含量不同造成的，低浓度变性剂对两种构象的影响不同，使拐点消失。ＫＣｌ可以改变两种构象的平衡

TWO NATIVE CONFORMATIONS OF CHICKEN LIVERDIHYDROFOLATE REDUCTASE

The urea-induced equilibrium unfolding transition of dihydrofolate reductase (DHFR) from chicken liver was well described by a two-state unfolding model involving only native and unfolded forms. But there are two phases in the kinetics study of denaturation of DHFR in 4.0mol/L urea which shows there must be additional species. Arrehius Plot of equilibrium DHFR has a discontinuity of slope, and in low concentrations of denaturant, the discontinuity disappeared. The possible explanation is that there are two native conformations of DHFR. The difference of unfolding rate constants between these two species accounts for the two phases in kinetics study. The denaturants affect the conformations of these two species in different extent. KCl canchange the equilibrium of two species.