Catalyzes the two-electron oxidation of bromide by hydrogen peroxide and generates hypobromite as a reactive intermediate which mediates the formation of sulfilimine cross-links between methionine and hydroxylysine residues within an uncross-linked collagen IV/COL4A1 NC1 hexamer. In turns, directly contributes to the collagen IV network-dependent fibronectin/FN and laminin assembly, which is required for full extracellular matrix (ECM)-mediated signaling. Thus, sulfilimine cross-links are essential for growth factor-induced cell proliferation and survival in endothelial cells, an event essential to basement membrane integrity. In addition, through the bromide oxidation, may promote tubulogenesis and induce angiogenesis through ERK1/2, Akt, and FAK pathways. Moreover brominates alpha2 collagen IV chain/COL4A2 at 'Tyr-1485' and leads to bromine enrichment of the basement membranes. In vitro, can also catalyze the two-electron oxidation of thiocyanate and iodide and these two substrates could effectively compete with bromide and thus inhibit the formation of sulfilimine bonds. Binds laminins. May play a role in the organization of eyeball structure and lens development during eye development.