稀土离子对烟草RuBPcase的激活作用及EXFAS研究

EFFECTS OF RARE EARTH IONS (Ln3+) ON THE ACTIVITY OF TOBACCORuBPcase AND ITS EXFAS RESULT

研究了稀土离子（Ｌｎ３ ＋） 对烟草（Ｎｉｃｏｔｉａｎａ ｔａｂａｃｕｍ）１ ，５ － 二磷酸核酮糖羧化酶（ＲｕＢＰｃａｓｅ）活力的影响。结果表明，在该酶的反应体系中，用Ｌｎ３ ＋ 替代Ｍｇ２ ＋ ，烟草ＲｕＢＰｃａｓｅ 的活力随Ｌｎ３ ＋ 浓度的变化曲线呈双相效应， 即在高浓度时， Ｌｎ３ ＋ 抑制该酶活性； 低浓度的Ｌｎ３ ＋ 提高ＲｕＢＰｃａｓｅ 活性。其活化效应为轻稀土离子大于重稀土离子，但Ｌｎ３ ＋ 的活化效应低于Ｍｇ２ ＋ 。在有Ｍｇ２ ＋ 的反应体系中，Ｌｎ３ ＋ 在低浓度时也有提高ＲｕＢＰｃａｓｅ 活性的能力，提高幅度较低；而高浓度的Ｌｎ３ ＋ 显著地抑制酶活性。进一步对ＲｕＢＰｃａｓｅ － Ｌａ 二元复合物的ＥＸＦＡＳ 研究，证实Ｌａ３ ＋ 与ＲｕＢＰｃａｓｅ 氨基酸残基的Ｏ 原子键合，键长为２ ．５１?；Ｌａ３ ＋ 还与Ｓ 原子结合。最后对Ｌｎ３ ＋ 和ＲｕＢＰｃａｓｅ

The effects of rare earth ions (ln3+) on the activity of RuBPcase were studied. The results revealed that the curve of RuBPcase activity was apparently biphasic by using different concentration to replace Mg2+ in enzymatic reaction. The activation effects of La3+ and Ce3+ on RuBPcase were greater than Gd3+, but the activation effect of Ln3+ was lower than Mg2+. In enzymatic reaction system with Mg2+,Ln3+could activate RuBPcase at low concentration also, but they had strongly inhibitory function at high concentration. The EXFAS result of RuBPcase-La complex indicated that La was bound to oxygen atom of amino-acid residuel, the distance of La-O bound is 2.51?. The mechanism of molecular interaction between Ln3+ and RuBPcase was discussed.