Catalyzes the oxidation of sulfhydryl groups in peptide and protein thiols to disulfides with the reduction of oxygen to hydrogen peroxide. Plays a role in disulfide bond formation in a variety of extracellular proteins. In fibroblasts, required for normal incorporation of laminin into the extracellular matrix, and thereby for normal cell-cell adhesion and cell migration. O2 + 2 R'C(R)SH = H2O2 + R'C(R)S-S(R)CR' Binds 1 FAD per subunit. A small proportion is secreted, probably via a proteolytic cleavage that removes the membrane anchor. N-glycosylated. O-glycosylated on Thr and Ser residues. Belongs to the quiescin-sulfhydryl oxidase (QSOX) family.