稀土离子对烟草RuBPcase的激活作用及EXFAS研究

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 相互作用的分子机制进行讨论

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

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.