钙调神经磷酸酶在胍变性过程中活力及构象变化的比较

COMPARISION OF INACTIVATION AND CONFORMATIONAL CHANGES OF CALCINEURINE IN GuHCl

钙调神经磷酸酶（ＣａＮ）在盐酸胍溶液中的内源荧光、远紫外ＣＤ谱及剩余活力的变化提示：ＣａＮ的酶活力在胍浓度为０．５ｍｏｌ／Ｌ左右可完全丧失，同时伴有内源荧光强度的下降，３３３ｎｍ最大发射峰的红移（提示了色氨酸和酪氨酸残基的暴露）。比较不同胍浓度下牛脑ＣａＮ的失活与整体构象变化，表明酶的失活先于整体构象变化。在０．６ｍｏｌ／Ｌ胍溶液中，内源荧光变化的动力学过程只能测出一相，而酶失活的动力学过程为快、慢两相，快相动力学速度常数比整体构象变化速度常数大１－２个数量级，慢相失活速度常数与整体构象变化速度常数相近。提示低浓度胍可引起该酶的完全失活，活性部位的空间构象比整个酶分子的构象更易受到变性剂的扰乱。

The changes of intrinsic fluorescence, CD spectra and residual activity of CaN in Gu. HCl solution indicated that CaN would be entirely inactivated in 0. 5mol/L Gu·HCl solution accompanied with the decrease of fluorescence intensity and a red shift from 333nm to 345nm of the maximum emission (showing the exposing of Trp and Tyr residue CaN). Comparing inactivation with conformational changes of CaN of bovine brain in different concentrations of Gu· HCl, a prior change of activity was shown. The changes in intrinsic fluorescence had only one kinetic stste, and the inactivation of enzyme had a fast process and a slow process.The rate constant of the fast process was 1-2 order of magnitude qreater than that of decreasing of intrinsic fluorescence while. The rate constant of the slow process was similar to that of conformational changes. Resalts suppest that the entire inactivation of CaN may be caused in low concentration of Gu·HCl solution and the conformation of active site was easier to be disturbed by denaturants than that of the enzyme.