| It has been established that both flavin and metal sulfhydryl oxidases catalyze the formation of disulfide bonds from cysteine residues with the reduction of oxygen to hydrogen peroxide. One specific enzyme, a metalloenzyme from bovine milk, has been extensively characterized by the Swaisgood laboratory (Janolino, V.G. and Swaisgood, H.E. (1975) J. Biol. Chem. 250, 2532-2537). With new evidence in hand, a study was carried out to purify and analyze a flavin sulfhydryl oxidase activity in bovine milk. This activity was linked to an enzyme that was insensitive to EDTA, required greater than 15,000-fold purification, contained no iron, and was identified by LC-MS/MS to be a member of the Quiescin-Sulfhydryl Oxidase enzyme family. Herein we discuss the implications of this study in comparison to the data available for the iron-containing sufhydryl oxidase already reported in bovine milk. |
