 In biology, disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins.The connection is a persulfide, in analogy to its congener, peroxide (R−O−O−R′), but this terminology is rarely used, except in reference to hydrodisulfides (R−S−S−H compounds).In inorganic chemistry disulfide usually refers to the corresponding anion (−S−S−).