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首页> 外文期刊>Biochemistry >Photoexcitation of Tryptophan Groups Induces Reduction of Two Disulfide Bonds in Goat alpha-Lactalbumin.
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Photoexcitation of Tryptophan Groups Induces Reduction of Two Disulfide Bonds in Goat alpha-Lactalbumin.

机译：色氨酸基团的光激发诱导山羊α-乳清蛋白中两个二硫键的还原。

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摘要

Illumination of goat alpha-lactalbumin (GLA) with 280 or 295 nm light results in tryptophan-mediated photolysis of disulfide bonds within the protein. The photolysis is not dependent on the absence or presence of Ca(2+) and is observed as well on illumination of native and of partially unfolded GLA. However, photolysis of native GLA results in a partial unfolding of the protein. The latter phenomenon is most clearly observed on fluorescence measurements at low temperatures (near 3 degrees C). The photolysis induces some dimerization and oligomerization, but most GLA molecules remain monomeric. To obtain more information about the reaction products, the illuminated protein is treated with iodoacetamide to label the free thiol groups, it is fragmented with trypsin, and the fragments are analyzed by mass spectrometry. Via this approach, we observe that the cleavage of disulfide bonds is restricted to Cys6-Cys120 and Cys73-Cys91 bonds. The photolytic cleavage of either of these disulfide bonds results in the formation of a single free thiol, a phenomenon restricted to Cys120 and Cys91, respectively. We also found indications that a thioether linkage is formed between Cys73 and Trp60. The alkylsulfenylation of Trp60 presumably results from a combination of primary thiyl and tryptyl radicals.
机译：用280或295 nm的光照射山羊α-乳白蛋白（GLA）会导致色氨酸介导的蛋白质中二硫键的光解。光解作用不依赖于Ca（2+）的存在或不存在，并且在自然和部分未折叠的GLA的光照下也可以观察到。然而，天然GLA的光解导致蛋白质的部分展开。在低温（接近3摄氏度）的荧光测量中，可以最清楚地观察到后一种现象。光解会引起一些二聚和低聚，但大多数GLA分子仍然是单体。为了获得有关反应产物的更多信息，用碘乙酰胺处理被照射的蛋白质以标记游离的硫醇基团，用胰蛋白酶使其片段化，然后通过质谱分析片段。通过这种方法，我们观察到二硫键的裂解仅限于Cys6-Cys120和Cys73-Cys91键。这些二硫键中的任何一个的光解均导致单个游离硫醇的形成，这种现象分别限于Cys120和Cys91。我们还发现了在Cys73和Trp60之间形成硫醚键的迹象。 Trp60的烷基亚磺酰化大概是伯硫基和胰基的结合。

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