岩豆凝集素的圆二色性与生物学活性关系的研究

岩豆凝集素（ＭＤＬ）的远紫外圆二色性谱（ＣＤ谱）显示２１６－２１７ｎｍ处的单一负峰。此时ＭＤＬ分子含有１６．２％的α螺旋，４６．３％的β折叠和３７．５％的无规卷曲。ｐＨ９．０时负峰红移至２２０ｎｍ，且在２１７－２２２ｎｍ处的峰值几乎相同；在２０－４０℃范围内，ＣＤ谱的变化甚微；６０℃时谱峰蓝移；在８０℃或１００℃时，２１２ｎｍ处出现一大负峰。１ｍｏｌ／Ｌ或２ｍｏｌ／Ｌ脲时，ＭＤＬ的ＣＤ谱已发生明显变化，二级结构单元也有变化，凝集兔红细胞的活性也随之减弱；随脲浓度的增加，ＭＤＬ的谱峰蓝移，最终在２１２ｎｍ处出现大负峰。当胍浓度为０．７５ｍｏｌ／Ｌ时，ＭＤＬ的ＣＤ谱即有明显变化和活性丧失；胍浓度继续增加，ＣＤ谱逐渐成为特征的无规卷曲的谱形。在ｐＨ９．０、温度超过８０℃、脲或胍浓度分别高于２ｍｏｌ／Ｌ和０．７５ｍｏｌ／Ｌ时，ＭＤＬ的ＣＤ谱发生显著变化的同时，其凝集兔红细胞的生物学活性全部丧失，分子的二级结构单元也发生很大改变。

The Studies on The CD Spectra and Hemagglutinating Activity of Millettia dielsiana Harms Lectin

Millettia dielsiana Harms Lectin(MDL) exhibits a characteristic circular dichroic(CD) spectral negative band centered at 217nm, thus it is estimated to contain about 16. 2%α-helix,46.3%β-pleated sheet and 37. 5% random coil. At pH9. 0,the negative band is redshift to 220nm. Temperature within the range of 20℃40℃ causes almost no change of the CD spectra of MDL, but the band is blueshift at temperature above 60℃, and leads to a large negative band centered at 212nm at the temperature above 80℃. The CD spectra of MDL are apparently changed in lmollL or ZmollL urea,so the secondary structure is also changed and the hemagglutinating activity is weaker.The band is blue-shift with the increase of urea concentration, and leads to a large negative band centered at 212nm. In 75mol/L guanidine,the hemagglutinating activity is lost and the CD spectra of MDL is obvious changed. MDL exhibits a characteristic CD spectra band of random coil with the increase of guanidine concentration. The studies show that MDl is inactive at pH9.0, temperature above 80℃ and the concentrations of urea and guanidine higher than 2mol/L and 0.75mol/L respectively with the apparent changes of CD spectra of MDL ,thus the secondary structure of MDL is also changed.