苦参凝集素的色氨酸残基修饰与荧光光谱研究

苦参凝集素（SFL）经等电聚焦测得其等电点为5.56，用比色法测得每分子SFL含有3个色氨酸残基，经N-溴代丁二酰亚胺（NBS）修饰表明其中2个Trp残基位于分子表面，当这2个Trp残基补修饰后，SFL的凝血活性完全丧失，糖保护试验表明，SFL专一性抑制糖Man能够保护SFL，阻断NBS对SFL的修饰作用，说明色氨酸不仅是SFL凝血活性所必需的，而且还参与其糖结合部位的组成，SFL随着NBS的逐渐修饰，其内源荧光光谱亦相应发生变化，结果表明分子表面的2个Trp残基可能位于分子的疏水袋中，而另一个Trp残基则埋藏于分子内部，荧光淬灭研究表明，丙烯酰胺能淬灭87%色氨酸残基的荧光。

STUDY ON TRYPTOPHAN MODIFICATION AND FLUORESCENCE SPECTRUM OF SOPHORA FLAVESCENS LECTIN

The isoelectric point of Sophora flavescens Lectin(SFL) was 5 56,determined by isoelectrofocusing There were 3 Trp residues in SFL molecule Native SFL had 2 exposed Trp residues,modification of which with N bromosuccinimide led to complete loss of the hemagglutinating activity of the Lectin Treatment of SFL in the presence of Mannose could protect the Trp residues from oxidation with a retention of a fairly high hemagglutinating activity These results indicate that Trp residues were essential for the hemagglutinating activity of SFL and were involved in carbohydrate binding site Modification of Trp residues with N bromosuccinimide induced changes in the fluorescence properties of SFL The changes implied that the 2 Trp residues in the surface of SFL were located in the hydrophobic pocket of the glycoprotein and the other Trp residue was buried in the interior of SFL The study on fluorescence quenching showed that the fluorescence from Trp residues were not quenched by KI,but 87% were quenched by acrylamide