Maeda H, Hattori H, Kanoh H
Department of Chemistry, Faculty of Science, Nagoya University, Japan.
Int J Biol Macromol. 1989 Oct;11(5):290-6. doi: 10.1016/0141-8130(89)90022-6.
Increase of the beta sheet content and aggregation of concanavalin A (con A) induced at about 60 C were followed with circular dichroism (c.d.) and scattered light intensity (I90) on both metal-complexed and demetallized species. The conversion occurred at a higher temperature for metal-complexed species than for demetallized one. A concentration-independent conversion curve of metal-complexed species, obtained for a concentration range below around 6 microgram/ml (6 x 10(-3) kg m-3) with a midpoint at 57 degrees C, was well described in terms of a conformational equilibrium between two conformers. However, aggregation did exist even at a low concentration of 1 microgram/ml. Aggregation also occurred without the conformational change as found at the initial stage or in Tris buffer, which suggested the absence of direct coupling between the conformational change and the aggregation. Changes of c.d. at 222 nm, expected to represent the main chain conformation, differed from those at 290 nm reflecting the environment of side chain chromophores. Time courses of three properties examined, c.d. at 222 nm, at 290 nm, and I90, always exhibited a lag in the case of metal-complexed species while the lag was not observed in the case of demetallized species, however. Lag became longer in c.d. but it became shorter in I90 as the protein concentration increased.
在大约60℃下诱导伴刀豆球蛋白A（伴刀豆凝集素A，Con A）的β-折叠含量增加和聚集，通过圆二色性（c.d.）和散射光强度（I90）对金属络合型和脱金属型物种进行监测。金属络合型物种的转变发生温度高于脱金属型物种。对于浓度低于约6微克/毫升（6×10⁻³千克/立方米）的金属络合型物种，获得了一条与浓度无关的转变曲线，中点温度为57℃，这可以用两种构象体之间的构象平衡很好地描述。然而，即使在1微克/毫升的低浓度下也存在聚集现象。在初始阶段或Tris缓冲液中，聚集也会在没有构象变化的情况下发生，这表明构象变化和聚集之间不存在直接耦合。预期代表主链构象的222纳米处的c.d.变化与反映侧链发色团环境的290纳米处的变化不同。所检测的三种性质的时间进程，即222纳米处、290纳米处的c.d.以及I90，在金属络合型物种的情况下总是表现出滞后现象，而在脱金属型物种的情况下未观察到滞后现象。随着蛋白质浓度的增加，c.d.的滞后时间变长，但I90的滞后时间变短。
