金黄色葡萄球菌核酸酶及其类似物盐酸胍变性的活力与构象变化的比较

金黄色葡萄球菌核酸酶（ＳｔａｐｈｌｏｃｏｃｃａｌＮｕｃｌｅａｓｅ，ＳＮａｓｅ）与其类似物（ＳＮａｓｅＲ）的平衡态盐酸胍变性与复性曲线及比活力值均无明显差别。两者变性与复性的构象变化是可逆的，但活力恢复滞后于失活。低浓度盐酸胍对ＳＮａｓｅＲ有２０％左右的激活，而低浓度（０．１２５ｍｏｌ／Ｌ）的ＮａＣｌ可使ＳＮａｓｅＲ的活力提高近一倍。ＳＮａｓｅＲ盐酸胍变性的失活先于构象变化。比较加入底物竞争抑制剂脱氧胸腺嘧啶核苷３＇－５＇－二磷酸（ｐｄＴｐ）后得到的（ＳＮａｓｅＲ＋ｐｄＴｐ＋Ｃａ２＋）三元络合物平衡态盐酸胍变性的Ｔｒｐ与Ｔｙｒ内源荧光的变化，观测到该酶的活性部位先于整体构象发生变化，结果导致ｐｄＴｐ解离常数Ｋｄ增大．

COMPARISON BETWEEN GUANDINUM-INDUCED ACTIVTTY AND CONFORMATION CHANGES OF STAPHYLOCOCCAL NUCLEASE AND ITS ANALOGUE

There were no difference in unfolding or refolding conformational tansition curves and specific activity between staphylococcal nuclease(SNase)and its analogue (SNaseR).Their unfolding and refolding conformational transition curves were overlapped, but their reactivition were lagged of inactivition. Low concentration of guanidinium shoal an activition of 20%,and 0.125mol/L sodium chloride showed an activition of nearly 100%.Compared the intrinsic fluorescence of tryptophan with tyrosine of the tertiary complex, formed by SNaseR,deoxythymidine-3'-5'-diphosphate (pdTp) and Ca2+, during equilibrium unfolding induced by guaniddrium, it was found that the conformation of active site of SNaseR was changed prior tO its conformational structare as a Whole, resulting in the enhance of the dissociation constant, Kd, between SNaseR and its competitive inhibitor pdTp.