亚硒酸钠诱导的晶状体蛋白质聚合作用

不仅在体内,而且在体外亚硒酸钠可引起晶状体蛋白质聚合。将亚硒酸钠加到pH7.4的晶状体蛋白质溶液中,在37℃保温30min后观察到蛋白质溶液变混浊,随时间的延长混浊程度加重并有沉淀形成。经SDS聚丙烯酰胺凝胶电泳发现,加硒保温后形成的不溶性蛋白质中有大量的高分子聚合物。当加入二硫苏糖醇后混浊的蛋白质溶液变清,其中的高分子聚合物也基本消失,我们还发现;在亚硒酸钠使晶状体蛋白质变混浊的同时,蛋白质巯基减少,而蛋白质结合的硒量增加,且二者之间有较固定的比例关系,即蛋白质上每增加一个硒原子,蛋白质巯基就减少4.26个。当用二硫苏糖醇还原后,68％的硒从蛋白质中释放出来。这些结果表明,亚硒酸钠可引起大鼠晶状体水溶性蛋白质聚合,其可能方式如下:4PSH+SeO_3~-→PSSP+PS-Se-SP+H_2O+2OH~-这可能是亚硒酸钠诱发白内障的主要原因。

The Aggregation of Rat Soluble Lens Proteins Caused by Sodium Selenite

In the sodium selenite induced cataractous lenses the contents of low molecular weight proteins decreased and that of high molecular weight proteins increased. This indicated that sodium selenite might cause lens protein to aggregate. Here we studied the aggregation of rat lens protein caused by sodium selenite in vitro, when sodium selenite was added to the solution of soluble lens proteins and incubated at 37℃ for a period, this solution became opaque. The opacity correlated to the concentration of sodium selenite.SDS-PAGE showed that there are high molecular weight aggregaes in the opaque solution. When the opaque solution was treated with dithiothreitol it became clear, and the high molecolar aggregates disappeared too.We found also that in the process of incubation the content of protein sulfhydryl group decreased and the content of protein bound selenium increased. The amount of sulf-hydryl group decreased corresponded to that of protein bound selenium increased,that is, with the increase of one atom of selenium, there would be 4.26 sulfhydryl groups decreased. About 68% of the protein bound selenium would be released if the protein was treated with dithiothreitol.So a conclusion was made as follow.4PSH + SeO3→PSSP + PS-Se-SP + H2O + 20H-This perhaps is the main cause of insolubilization of lens protein induced by sodium selenite and may be the mechanism of cataract formation induced by selenite.