Pazos I F, Alvarez C, Lanio M E, Martinez D, Morera V, Lissi E A, Campos A M
Department of Biochemistry, Faculty of Biology, University of Havana, Cuba.
Toxicon. 1998 Oct;36(10):1383-93. doi: 10.1016/s0041-0101(98)00016-6.
Sticholysin II is a highly hemolytic toxin present in the caribbean sea anemone Stichodactyla helianthus. Pre-incubation of St II with 2,2'-azobis(2-amidinopropane), a source of peroxyl radicals in air saturated solution, readily reduces its hemolytic activity. Analysis of the amino acids present in the protein after its modification shows that only tryptophan groups are significantly modified by the free radicals. According to this, the loss of hemolytic activity correlates with the loss of the protein intrinsic fluorescence. The results indicate that, at high toxin concentrations, nearly a tryptophan residue and 0.2 toxin molecules are inactivated by each radical introduced into the system. Association of St II to multilamellar liposomes (egg yolk phosphatidyl choline:sphingomyelin 1:1) increases the toxin intrinsic fluorescence, indicating a more hydrophobic average environment of the five tryptophan groups of the protein. In agreement with this, incorporation of St II to the liposomes reduces the rate of fluorescence loss during its modification by free radicals, particularly at long incubation times. These results are explained in terms of two populations of tryptophans that are quenched at different rates by acrylamide and whose rates of inactivation by free radicals are also different.
刺参溶细胞素II是一种存在于加勒比海海葵日光海葵中的高溶血毒素。在空气饱和溶液中，将刺参溶细胞素II与过氧自由基源2,2'-偶氮二(2-脒基丙烷)预孵育，会使其溶血活性迅速降低。对修饰后的蛋白质中存在的氨基酸进行分析表明，只有色氨酸基团会被自由基显著修饰。据此，溶血活性的丧失与蛋白质固有荧光的丧失相关。结果表明，在高毒素浓度下，系统中每引入一个自由基，就会使近一个色氨酸残基和0.2个毒素分子失活。刺参溶细胞素II与多层脂质体（蛋黄磷脂酰胆碱:鞘磷脂1:1）结合会增加毒素的固有荧光，这表明该蛋白质的五个色氨酸基团所处的平均环境更疏水。与此一致的是，将刺参溶细胞素II掺入脂质体会降低其在被自由基修饰过程中的荧光损失速率，尤其是在长时间孵育时。这些结果可以用两类色氨酸来解释，它们被丙烯酰胺淬灭的速率不同，被自由基失活的速率也不同。
