 In equivalent terms, it catalyzes the oxidation of a pair of cysteine residues on the substrate protein.Most of the substrates for DsbA are eventually secreted, and include important toxins, virulence factors, adhesion machinery, and motility structures DsbA is localized in the periplasm, and is more common in Gram-negative bacteria than in Gram-positive bacteria.Within the thioredoxin family, DsbA is the most strongly oxidizing member.