A flavin-dependent sulfhydryl oxidase in bovine milk
A flavin-dependent sulfhydryl oxidase in bovine milk
复制标题
DOI：
10.1021/bi7016975
复制
发表时间：
2007-11-13
期刊：
影响因子：
2.9
通讯作者：
Thorpe, Colin
中科院分区：
文献类型：
--
作者：
Jaje, Jennifer;Wolcott, Holly N.;Thorpe, Colin
金属和黄素依赖的巯基氧化酶都催化氧还原为过氧化氢，从而净生成二硫键。第一个被描述的哺乳动物巯基氧化酶是从牛乳乳清中分离出来的一种依赖铁的酶(Janolino，V.G.和SwisGood，H.H.(1975)J.Biol)。化学。250、2532-2537)。据报道，该蛋白每89 kDa亚基含有0.5个铁原子，并被乙二胺四乙酸酯(EDTA)完全抑制。然而，目前的工作表明，在脱脂牛奶中，FAD连接的、对EDTA不敏感的、可溶的62 kDa的巯基氧化酶显然是主要的二硫键生成活性。与金属酶不同，黄素蛋白与脱脂乳膜没有紧密的联系。纯化的牛酶(>；70%覆盖率)的测序表明它是Quiescin-巯基氧化酶(QSOX)家族的成员。与其溶解性一致的是，这种牛QSOX1类似物缺乏这些长形式蛋白质的C-末端跨膜跨度。牛乳QSOX1对还原的核糖核酸酶和模型底物二硫苏糖醇具有很高的活性。这些新发现的意义与金属依赖的巯基氧化酶的早期报道有关。
Both metal and flavin-dependent sulfhydryl oxidases catalyze the net generation of disulfide bonds with the reduction of oxygen to hydrogen peroxide. The first mammalian sulfhydryl oxidase to be described was an iron-dependent enzyme isolated from bovine milk whey (Janolino, V.G., and Swaisgood, H.E. (1975) J. Biol. Chem. 250, 2532-2537). This protein was reported to contain 0.5 atoms of iron per 89 kDa subunit and to be completely inhibited by ethylenediaminetetraacetate (EDTA). However the present work shows that a soluble 62 kDa FAD-linked and EDTA-insensitive sulfhydryl oxidase apparently constitutes the dominant disulfide bond-generating activity in skim milk. Unlike the metalloenzyme, the flavoprotein is not associated tightly with skim milk membranes. Sequencing of the purified bovine enzyme (>70% coverage) showed it to be a member of the Quiescin-sulfhydryl oxidase (QSOX) family. Consistent with its solubility, this bovine QSOX1 paralogue lacks the C-terminal transmembrane span of the long form of these proteins. Bovine milk QSOX1 is highly active toward reduced RNase and with the model substrate dithiothreitol. The significance of these new findings is discussed in relation to the earlier reports of metal-dependent sulfhydryl oxidases.