A Flavin-Dependent Sulfhydryl Oxidase in Bovine Milk

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• 作者：Jennifer Jaje ; Holly N. Wolcott ; Olajumoke Fadugba ; Diane Cripps ; Austin J. Yang ; Ian H. Mather ; Colin Thorpe
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：November 13, 2007
• 年：2007
• 卷：46
• 期：45
• 页码：13031 - 13040
• 全文大小：271K
• 年卷期：v.46,no.45(November 13, 2007)
• ISSN：1520-4995

文摘

Both metal and flavin-dependent sulfhydryl oxidases catalyze the net generation of disulfidebonds with the reduction of oxygen to hydrogen peroxide. The first mammalian sulfhydryl oxidase to bedescribed 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 per89 kDa subunit and to be completely inhibited by ethylenediaminetetraacetate (EDTA). However thepresent work shows that a soluble 62 kDa FAD-linked and EDTA-insensitive sulfhydryl oxidase apparentlyconstitutes the dominant disulfide bond-generating activity in skim milk. Unlike the metalloenzyme, theflavoprotein 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. Consistentwith its solubility, this bovine QSOX1 paralogue lacks the C-terminal transmembrane span of the longform of these proteins. Bovine milk QSOX1 is highly active toward reduced RNase and with the modelsubstrate dithiothreitol. The significance of these new findings is discussed in relation to the earlier reportsof metal-dependent sulfhydryl oxidases.